Vary. 


PUB-  y 


REPORT 


APPOINTED  TO  RKCOMMEXD  A  PLAN  FOR  THE 


NEW  YORK  AND  LONG  ISLAND  BRIDGE 


ACROSS  THE  EAST  RIVER, 


Blackwell's  Island. 


New  York ; 

X  UK    GRAPHIC    COMPAN  Y, 

39  &  41  Park  Place. 


Avery  Architectural  and  Fine  Arts  Library 
Gift  of  Seymour  B.  Durst  Old  York  Library 


REPORT 


OF 


APPOINTED  TO  RECOMMEND  A  PLAN  FOR  THE»° 


NEW  YORK  AND  LONG  ISLAND  BRIDGE 


ACROSS  THE  EAST  RIVER, 


Blackwell's  Island. 


New  York: 

THK    GRAPHIC  COMPANY, 

39  &  41  Park  Place. 


Entered  according  to  act  of  Congress,  in  the  year  1877,  by  the 
NEW  YORK  AND  LONG  ISLAND  BRIDGE  CO., 
In  the  office  of  the  Librarian  of  Congress,  at  Washington,  D.  C. 


REPORT 


New  York,  February  21,  1877. 


To  the  President  and  Directors  of  the  New  York  and  Long 
/stand  Bridge  Company : 

Gentlemen  : — Upon  being  appointed  a  board  of  consulting- 
engineers,  on  the  10th  of  December,  1875,  for  the  purpose  of 
recommending  a  design  for  your  proposed  bridge  across  the  East 
River  at  BlackwelPs  Island,  the  undersigned  at  once  entered 
upon  an  examination  of  the  plans  then  in  the  possession  of  the 
Company. 

These  plans  formed  eleven  sets  or  designs,  and  had  been 
submitted  by  the  following  gentlemen  : 


Mr.  C.  Bender, 
Messrs.  Flad  &  Pfeifer, 
Mr.  J.  B.  Eads, 
Mr.  W.  P.  Trowbridge, 
Mr.  E.  W.  Serrell, 
Mr.  G.  E.  Harding, 


Mr.  I.  D.  Coleman, 

The  Baltimore  Bridge  Co., 

The  Watson  Manuf.  Co., 

Mr.  A.  F.  Wendt, 

Mr.  L.  W.  Wright. 


Most  of  these,  however,  were  more  in  the  nature  of  prelimin- 
ary studies  than  of  matured  designs,  and  few  of  them  were 
accompanied  with  the  necessary  strain  sheets,  computations  of 
quantities,  or  estimates  of  cost.  None  were  backed  up  by  pro- 
posals for  construction  at  a  specified  price. 


4 


A  short  examination  showed  not  only  that  these  plans  were 
fragmentary,  but  that  they  were  based  upon  different  assump- 
tions ;  either  as  to  the  traffic  to  be  accommodated,  the  loads  to 
be  provided  for,  or  the  safe  limit  of  strength  of  the  materials  to 
be  employed. 

That,  in  fact,  each  plan  was  predicated  on  a  different  specifi- 
cation ;  some  of  them  not  being  in  accordance  with  the  well- 
settled  principles  which  govern  the  distribution  of  forces  in 
bridge  structures,  and  thus  conducing  to  unsafe  constructions. 

It  became  evident,  therefore,  that  the  Board  of  Consulting 
Engineers  must  first  state  some  general  basis  as  to  the  arrange- 
ment of  the  bridge  and  its  approaches,  and  lay  down  some 
general  rules  and  principles  to  govern  the  designers,  before  the 
merits  of  their  plans  could  be  compared  with  each  other. 

Some  additional  surveys,  which  were  found  necessary,  were 
accordingly  made,  and  a  set  of  specifications  carefully  prepared, 
a  copy  of  which  is  hereto  attached,  marked  Appendix  No.  i. 

A  profile  of  the  ground  and  grades  was  also  published,  which 
is  herewith  given  as  Appendix  No.  2. 

These  provided  not  only  for  a  railroad  connection  across  the 
bridge,  but  for  main  and  return  approaches  for  carriage  ways, 
and  also  for  passenger  elevators  at  the  abutments,  so  as  to  give 
access  to  the  bridge  from  all  the  points  that  seemed  to  promise 
traffic. 

A  circular  was  issued  on  the  1st  of  May  inviting  designs  to 
be  handed  in  by  the  1st  of  July,  1876,  a  copy  of  which  forms 
Appendix  No.  3.  This  was  sent  to  nineteen  bridge  builders 
and  designers  and  to  some  forty  other  persons,  most  of  whom 
are  civil  engineers  or  bridge  experts. 

Answers  were  received  from  some  twenty  persons  expressing 
the  intention  to  furnish  plans  ;  but  the  completeness  of  the  in- 
formation called  for  by  the  specifications,  the  shortness  of  the 
time  allowed,  and  the  uncertainty  then  thought  to  exist  about 
the  future  construction  of  the  bridge,  deterred  the  designers  from 
perfecting  their  plans  by  the  specified  time. 

Upon  our  report  to  your  board,  a  resolution  was  passed  by 
you,  on  the  9th  of  August,  extending  the  time  for  receiving  de- 
signs to  the  1st  of  December,  1876,  and  offering  three  premiums 
of  $1,000,  $500  and  $250,  respectively,  for  the  first,  second  and 
third  best  plans  to  be  presented.    The  circular  issued  by  us  in 


5 


accordance  with  this  resolution  is  given  in  Appendix  No.  4. 
A  copy  was  sent  to  each  of  the  gentlemen  who  had  previously 
been  invited  to  furnish  designs,  and  to  a  number  of  other  par- 
ties who  applied  for  it. 

By  the  10th  of  December  nine  sets  of  plans  and  designs  had 
been  received,  with  more  or  less  explanatory  information. 
Much  of  this  information,  however,  was  found  incomplete  and 
insufficient.  In  some  instances  strain  sheets  were  not  furnished, 
or  else  they  did  not  provide  for  all  the  various  strains  due  to 
different  conditions  of  loads  and  wind.  Some  computations  of 
quantities  were  not  given,  and  the  estimates  did  not  show  the 
quantities  and  prices  of  material,  so  that  they  might  be  checked 
over  and  a  judgment  passed  upon  their  sufficiency. 

It  became  necessary,  therefore,  to  call  for  the  lacking  inform- 
ation. This  was  done  at  once  ;  and  the  Board,  having  been 
enabled  to  secure  the  services  of  Mr.  C.  C.  Schneider,  an 
engineer  of  experience  in  bridge  construction,  to  verify  the 
strain  sheets  and  check  over  the  various  computations,  entered 
upon  the  examination  of  the  plans  and  the  information  received. 

Much  of  the  additional  information  asked  for  came  in  very 
slowly  ;  some  of  it,  in  fact,  is  not  yet  received  ;  but  enough  has 
been  secured  in  every  case  to  obtain  a  proper  understanding  of 
the  designs  presented,  and  to  form  a  judgment  as  to  their  adapt- 
ation to  the  local  circumstances  and  surroundings  of  the  loca- 
tion, and  to  their  relative  economy. 

The  plans  received  may  be  classified  and  described  as  fol- 
lows : 


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8 


The  chief  feature  of  interest  and  novelty  about  your  proposed 
bridge  is  the  fact  that  spans  of  734  and  618  feet,  respectively, 
are  required  across  the  two  arms  of  the  East  River,  at  an  eleva- 
tion of  at  least  130  feet  above  one  of  the  most  busily  navigated 
streams  in  this  country.  These  great  spans,  although  forming 
but  one-eighth  of  the  total  length  of  the  structure,  will  cost  con- 
siderably more  than  one-half  of  the  whole,  and,  with  one  single 
exception,  are  unprecedented  for  railroad  purposes.  The  Niag- 
ara Suspension  Bridge,  of  800  feet  clear  span,  alone  surpasses 
the  length  of  the  proposed  spans,  while  the  following  railroad 
bridges  approach  this  magnitude : 

The  Cincinnati  Southern  Bridge,  truss,  517  feet  span  clear. 
The  St.  Louis  Bridge,  braced  arch,  .  515  feet  span  clear. 
The  Kuilenburg  Bridge,  trussed  girder,  493  feet  span  clear. 
The  Britannia  Bridge,  tubular  girder,  .  460  feet  span  clear. 
Saltash  Bridge,  double  bowstring  girder,  455  feet  span  clear. 
The  Cincinnati  Bridge,  truss,  .  .  .  420  feet  span  clear. 
The  Louisville  Bridge,  trussed  girder,  .  400  feet  span  clear. 
The  Diershau  Bridge,  lattice  girder,  .  398  feetTspan  clear. 
The  Conway  Bridge,  tubular  girder,      .      400  feet  span  clear. 

Our  examinations  of  the  strains  and  computations,  therefore, 
have  principally  been  directed  to  the  plans  for  the  two  long 
spans ;  and  although  we  have  also  given  due  attention  to  those 
for  the  approaches  and  lesser  spans,  our  discussion  of  the  merits 
and  demerits  of  the  various  designs  will  here  mainly  be  con- 
fined to  those  proposed  for  the  stretches  across  the  East  River, 
as  these  form  the  most  novel  and  costly  features  of  your  struc- 
ture. 

The  remainder  of  the  work  is  of  no  unusual  character,  and 
the  requirements  are  readily  provided  for  by  the  types  of  metal- 
lic structures  in  common  use. 


DISCUSSION  OF  PLANS. 

I.  The  plan  submitted  by  Mr.  L.  W.  Wright  for  the  long 
spans  consists  of  a  species  of  lattice  girder,  with  considerable 
cambre,  as  shown  on  plate  I. 

There  are  no  strain  sheets  or  estimates. 


c 
c 
c 


9 


We  feel  confident  that  were  the  designer  [to  make  a  careful 
and  correct  estimate  of  the  strains  developed  in  the  bridge  by 
its  own  weight,  he  would  essentially  modify  the  plan. 

II.  The  design  submitted  by  Mr.  G.  A.  Karwiese  for  the 
great  spans  consists  of  a  hinged  arch,  of  which  the  lower  mem- 
ber is  a  parabola  and  the  upper  member  is  slightly  cambred. 
The  upper  and  lower  members  are  composed  of  wrought-iron 
pipes,  and  the  general  arrangement  of  parts  is  shown  on  plate  II. 

Were  the  location  over  a  deep  chasm  with  natural  rocky 
abutments  high  above  the  stream, Tthe  main  features  of  this 
design  would  not  be  inapplicable,  and  ft  might  be  perfected  so 
as  to  be  economical.  The  hinging  of  the  parabolic  arch  at  the 
crown  and  at  the  abutment  would  eliminate  the  strains  from 
changes  of  temperature,  while  the  upper  member  would  impart 
rigidity.  The  necessity  for  building  abutments  up  from  the 
bottom,  at  the  proposed  location,  would,  however,  prove  some- 
what costly,  while  the  limitation  of  the  head  room  by  the 
haunches  of  the  arch  would  materially  obstruct  the  free  naviga- 
tion of  the  river,  and  probably  contravene  the  terms  of  the 
charter. 

The  side  elevation  of  the  longest  span  (which  the  designer 
proposes  to  make  760  feet  in  the  clear),  while  showing  a  height 
of  135  feet  at  the  apex,  gives  130  feet  of  head-room  for  a  length 
of  but  230  feet  in  the  centre,  and  of  only  97  feet  at  a  distance  of 
80  feet  from  the  abutments,  at  which  points  sailing  vessels  must 
occasionally  pass. 

The  method  proposed  for  placing  this  span  in  position — by 
raising  it  along  the  margin  of  the  river,  one  end  resting  on  a 
pivot  at  the  abutment,  and  the  other  on  floats,  and  of  afterwards 
swinging  it  across,  thus  describing  a  quarter  of  a  circle,  with 
the  abutment  as  a  pivot,  strikes  us  as  extra-hazardous.  It 
would  not  only  involve  temporary  obstruction  to  the  navigation, 
but  also  great  risk  of  disaster  and  wreck  to  the  entire  structure. 

These  objections  appear  to  us  so  serious  as  to  warrant  putting 
this  design  aside,  as  not  fulfilling  the  conditions  of  the  charter 
and  of  the  specifications. 

III.  The  design  presented  by  Mr.  W.  J.  Morris,  for  the  Cin- 
cinnati Bridge  Company,  consists,  for  the  great  spans,  of  a 


10 


braced  suspension  cable,  which  it  is  proposed  to  make  of  steel 
wire,  stiffened  by  two  parabolic  trusses  built  upon  them  and 
meeting  in  the  centre,  as  shown  on  plate  III. 

This  is  the  only  suspension  system  among  the  designs  pre- 
sented in  which  the  stiffening  members  are  so  arranged  as  to 
provide  for  a  rigid  railway  bridge.  Although  the  plans  are 
probably  too  defective  to  be  admissible  as  they  are,  they  yet 
present  the  excellent  features  of  providing  for  a  structure,  the 
parts  of  which  will  work  in  harmony  with  each  other,  and  in 
which  there  will  be  no  doubt  as  to  the  resulting  strains  coming 
upon  each  member.  To  insure  this,  however,  it  seems  to  us 
that  the  cables  should  be  hinged  at  the  centre  of  the  spans. 
The  designer  states  that  this  is  to  be  done,  but  the  plans  do  not 
show  how  it  is  to  be  accomplished,  and  it  seems  to  us  difficult 
to  apply  this  feature  to  a  wire  cable. 

The  details  of  the  design,  however,  are  so  imperfect  as  to 
preclude  us  from  recommending  it.  The  great  length  of  the 
back  stays  would  produce  a  rise  and  fall  of  4  3-10  feet  at  the 
centre  of  the  span  under  changes  of  temperature,  and  not  only 
has  the  dead  weight  of  the  structure  been  somewhat  under- 
estimated, but  there  are  serious  errors  in  the  computations  of 
strains,  under  certain  conditions  of  load,  the  rectification  of 
which  would  increase  the  quantities  of  materials  required  and 
the  estimate  of  cost. 

These  errors  and  deficiencies,  affecting  important  parts  of 
the  structure,  vitiate  the  design  to  such  an  extent  as  to  render 
it  inadmissible  under  the  specifications  and  circulars  inviting 
plans. 

IV.  Mr.  A.  Lucius  proposes  a  structure  which  conforms  very 
closely  to  the  existing  types  and  practice  for  ordinary  spans. 

The  approaches  are  on  iron  trestle-work,  and  the  great  spans 
are  standard  "  Pratt "  trusses,  modified  as  suggested  by  their 
own  dead  weight,  which  becomes  so  great  as  not  to  require 
counter-bracing  against  the  effects  of  the  live  load. 

A  sketch  is  shown  on  plate  IV. 

So  far  as  we  have  checked  them  over,  his  calculations  of 
strains  and  computations  of  quantities  are  correct,  and  the 
design  fulfils  all  the  conditions  of  the  specifications  as  to  sta- 
bility, strains  and  provisions  for  thoroughfares. 


11 


This  plan  well  illustrates  how  certain  types  of  bridges, 
well  adapted  to  certain  lengths  of  span,  become  uneconomical 
when  applied  to  greater  spans  and  other  circumstances  of 
location,  and  how  little  any  type  may  be  said  .to  be  absolutely 
the  best. 

Thus,  for  an  opening  under  20  feet  we  employ  a  simple  stick 
of  timber  or  an  iron  beam.  For  spans  of  about  40  feet,  plate 
girders  form  an  approved  construction  ;  while  for  stretches  from 
100  to  400  feet,  various  styles  of  trusses,  varying  somewhat  in 
design  and  arrangement  with  the  span,  have  been  found  best 
adapted  to  the  requirements  of  each  case. 

As  we  reach  spans  of  600  and  700  feet,  departures  from 
existing  practice  recommend  themselves,  and  the  types  adapted 
to  spans  even  as  great  as  400  and  500  feet  are  no  longer  the 
most  economical.  In  partial  recognition  of  this  fact,  various 
proposals  have  from  time  to  time  been  made  by  designers  for 
the  introduction  of  new  types  of  bridges.  Many  of  them  have 
proved  worthless,  and  inasmuch  as  the  opportunities  for  build- 
ing great  spans  are  very  rare,  such  of  them  as  possess  merit 
have  not  developed  the  advantages  and  economy  which  they 
would  show  for  long  spans,  in  the  short  spans  to  which  they 
have  been  applied. 

It  will  be  seen  that  Mr.  Lucius,  on  the  other  hand,  by  adher- 
ing too  closely  to  existing  types,  has  produced  a  design  which, 
whatever  its  other  merits,  cannot  be  said  to  be  cheap. 

The  cost  is  estimated  at  $2,523,072  for  a  single  track  bridge, 
without  the  tunnel,  while  there  are  at  least  four  designs  which 
will  cost  less  than  $2,000,000  for  the  same  elements. 

There  is,  moreover,  a  difficulty  and  danger  involved  in  the 
method  planned  for  placing  these  spans  in  position.  He  pro- 
poses to  erect  them  upon  the  land,  one  end,  however,  project- 
ing over  the  water;  to  place  that  end  on  a  float  (the  greater 
span  complete  weighs  4,418,000  pounds)  and  to  haul  it  across 
the  channel,  rolling  it  out  over  the  abutment,  until  it  reaches 
its  final  position.  He  estimates  that  this  operation  would 
obstruct  the  navigation  no  more  than  one  day  for  each  span. 

This  seems  to  us  a  hazardous  undertaking,  and  in  view  of  pos- 
sible interference  from  passing  vessels,  from  wind  and  tide,  and 
unexpected  delays  and  difficulties,  one  upon  which  the  entire 
destruction  of  so  costly  a  structure  should  not  be  jeoparded. 


12 


We  would  not  advise  taking  so  great  a  risk,  even  if  the  struc- 
ture were  more  economical. 

V.  Mr.  W.  S.  Pope  proposes  for  the  Detroit  Bridge  Works 
a  suspension  bridge,  with  an  auxiliary  girder.  The  cables  are 
to  be  of  steel  wire,  and  the  form  of  the  long  spans  as  shown  on 
plate  V. 

The  information  accompanying  the  plans  is  more  full  and 
complete  than  any  other  which  we  have  received.  The  strain 
sheets,  computations  of  quantities,  and  description  of  parts  are 
so  intelligently  arranged  as  to  give  a  clear  idea  of  every  part 
of  the  design. 

We  cannot  agree,  however,  with  some  of  the  assumptions 
made  as  to  the  distribution  of  the  strains.  The  stiffening  girder 
which  carries  the  roadway  across  the  great  spans  is  suspended 
from  the  cable  and  also  from  a  series  of  inclined  stays,  which 
reach  about  one-half  of  the  distance  from  the  end  towers  to  the 
centre,  as  at  the  Niagara  Suspension  Bridge.  So  far  as  both 
of  these  systems  extend,  it  is  assumed  that  one-half  of  the  loads 
will  be  carried  by  the  cables  and  the  other  half  by  the  inclined 
stays.  These  form  two  distinct  and  independent  systems  of 
suspension,  and  there  is  no  evidence  whatever  that  the  load  at 
any  one  point  will  distribute  itself  in  the  particular  proportion 
assumed.  However  accurately  the  two  systems  may  be  ad- 
justed when  first  erected,  the  changes  of  temperature  are  sure 
to  change  their  relative  positions  and  lengths  and  to  vary  the 
relative  proportions  of  the  loads  which  they  bear.  This  is  the 
case  with  the  Niagara  Bridge,  the  contraction  of  the  cable  on  a 
cold  day  in  winter  raising  up  the  platform  and  taking  the  weight 
from  the  stays,  so  that  they  become  loose  and  are  visibly 
crooked.  The  cables  in  that  bridge  are  therefore  made  strong 
enough  to  do  all  the  work,  with  a  factor  of  safety  of  about  4^, 
and  the  stays  are  merely  relied  on  to  stiffen  the  truss. 

We  find,  moreover,  that  this  design  does  not  provide  for 
strains  arising  from  changes  of  temperature,  which  will  be  very 
considerable  in  the  long  spans. 

The  aggregate  cost  condemns  the  plan.  It  is  estimated  at 
$3,700,000,  without  the  tunnel.  It  is  fair  to  state,  however, 
that  this  includes  an  allowance  of  twenty  per  cent  to  cover 
engineering  and  contingencies,  and  that,  when  these  are  de- 


> 


- 


13 


ducted,  the  estimated  cost  stands  at  $3,066,400  for  a  single 
track  bridge,  leaving  it,  however,  still  the  most  expensive  struc- 
ture on  the  list. 

VI.  The  plans  submitted  by  E.  W.  Serrell  &  Son  provide 
for  a  suspension  bridge,  the  cables  of  which  are  composed  of 
wrought-iron  links,  which,  together  with  a  system  of  diagonal 
stays,  sustain  a  stiffening  girder,  as  shown  on  plate  VI. 

We  are  unable  to  agree  that  this  design  fulfils  the  require- 
ments of  the  specifications,  which  require  that  the  structure 
should  be  so  designed  as  to  provide  for  the  maximum  strains 
which  can  by  any  possibility  come  upon  any  part  of  the  bridge. 

The  designers  assume  that  all  the  dead  weight  of  the  struc- 
ture in  the  long  spans  will  be  carried  by  the  chain,  which  is  so 
far  right ;  but  they  also  assume  that,  in  that  portion  over  which 
both  systems  extend,  all  the  live  load  will  be  carried  by  the 
stays  as  far  as  they  go,  and  that  the  chain  will  carry  the 
remainder — t.  e.,  that  portion  of  the  live  load  which  comes 
between  the  ends  of  the  stay-rod  systems.  There  is  no  proof 
satisfactory  to  the  entire  Board  of  the  correctness  of  this 
assumption. 

Of  course,  in  planning  a  compound  structure  in  which  sev- 
eral systems  are  expected  to  carry  the  load,  as  in  the  case  of  a 
chain  and  diagonal  stays,  or  that  of  an  arch  and  truss,  it  is 
natural  to  assume  that  the  load  will  be  divided  in  some  ratio 
between  them,  but  in  such  cases  it  is  absolutely  necessary  for 
safety  that  each  should  be  made  strong  enough  to  bear  all  the 
load  which  can  by  any  possibility  come  upon  them  ;  and,  as  in 
the  case  under  consideration,  both  the  dead  and  the  live  loads 
are  mainly  concentrated  on  the  same  floor,  it  is  probable  that 
strains  resulting  from  both  will  follow  the  same  law  of  stability 
and  take  the  shortest  available  road  to  the  top  of  the  towers,  as 
governed  by  the  location  of  the  loads  and  the  adjustment  of  the 
bridge. 

The  calculations  of  strains  from  the  effect  of  the  live  load 
carried  by  the  cable  between  the  ends  of  the  stay-rod  systems 
and  those  due  to  the  wind  strains  for  the  towers  of  the  river 
spans  leave  much  to  be  desired. 

The  stiffening  trusses,  as  designed,  are  only  12%  feet  in 
depth.    This  is  thought  by  some  of  us  to  be  too  shallow,  and 


14 


that  it  would  make  the  middle  portion  of  the  spans  so  flexible 
that  its  parts  would  be  unduly  strained  if  trains  run  over 
(as  they  should)  at  full  speed. 

The  designers  propose  an  ingenious  arrangement  for  insuring 
the  working  in  unison  of  the  main  chains  and  of  the  stays  under 
changes  of  temperature.  They  propose  to  suspend  a  lever  from 
the  saddles  over  the  towers  and  to  attach  the  stays  to  a  series 
of  pivots  placed  on  the  line  of  this  lever,  so  placed  that  its 
movements  shall  compensate  for  the  different  contractions  and 
expansions  of  the  chains  and  stays  under  the  changes  of  tem- 
perature. We  are  not  prepared  to  say  that  this  would  or 
would  not  prove  efficient.  If  it  were  certain  that  all  the  vari- 
ous members  of  the  bridge  would  always  be  equally  exposed  to 
the  sun  and  equally  heated  and  cooled,  and  that  the  vertical 
motion  due  to  the  expansion  and  contraction  of  the  cable  and 
stiffening  girder  would  take  place  regularly,  instead  of  con- 
forming to  a  curve,  the  radius  of  which  changes  with  the 
temperature,  the  result  expected  by  the  designers  would  doubt- 
less follow.  Further  study,  however,  would  be  necessary 
before  we  could  venture  to  recommend  the  adoption  of  a 
method  which,  however  ingenious,  is  yet  an  untried  experiment. 

It  will  be  noticed  that  none  of  the  designs  which  have  been 
submitted  for  suspension  bridges  meet  the  requirements  of  the 
case  or  of  the  specifications.  This  arises  partly  from  deficien- 
cies in  the  designs  and  partly  from  the  difficulty  of  adapting 
this  system  to  the  necessities  of  the  traffic  to  be  accommodated, 
which  require  a  rigid  structure.  Suspension  bridges  wich  stiff- 
ening girders  have  been  largely  and  successfully  erected  for 
carriage  roads,  over  which  the  rolling  loads  are  light  and  pro- . 
ceed  at  low  speed,  thus  giving  a  flexible  structure  time  to  adjust 
itself  to  the  changing  position  of  the  weights  to  be  carried. 
When,  however,  the  heavy,  concentrated  loads  of  railway 
engines  and  trains  are  to  pass  at  high  speed  (as  they  ought  in 
a  bridge  two  miles  in  length,  so  costly  as  to  require  the  profits 
on  a  large  business  to  pay  interest  on  the  capital  invested)  the 
structure  should  be  so  rigid  as  not  to  be  disturbed  and  racked 
under  the  effects  of  the  live  load.  This  indispensable  rigidity 
may  be  conferred,  it  is  believed,  by  an  auxiliary  truss,  but  the 
very  rigidity  of  the  truss,  if  continuous,  prevents  its  working  in 
harmony  in  varying  states  of  temperature  with  the  cable,  if,  as 


4 


15 


in  the  road  bridges  we  have  alluded  to,  and  as  in  the  Niagara 
Bridge  (which  only  permits  slow  motions  of  trains),  the  truss 
is  continuous.  Hence  the  compulsory  resort  to  trusses  hinged 
at  the  centre.  This  arrangement,  or  others  hitherto  proposed 
(which  we  have  not  room  to  discuss),  involves  very  consider- 
able departure  from  the  ordinary  methods  of  suspension,  and 
none  of  the  designs  submitted  (except,  perhaps,  that  of  the  Cin- 
cinnati Bridge  Company)  seem  to  recognize  this  fact. 

VII.  The  design  of  Messrs.  Henry  Flad  &  Co.  consist,  for 
the  large  spans,  of  straight  link  suspension,  or,  more  properly 
speaking,  derrick  bridges,  which  are  planned  for  a  double 
track  throughout,  including  the  approaches. 

A  sketch  of  the  main  span  is  shown  on  plate  VII. 

The  difficulty  in  preventing  the  long  suspension  links  from 
sagging  down  from  a  straight  line  by  their  own  weight  and 
thus  destroying  the  theoretical  adjustment  of  the  bridge,  is  quite 
ingeniously  met  by  a  system  of  braces  and  ties,  which  unite  all 
the  links  by  circular  arcs  and  prevent  their  becoming  catenaries 
instead  of  straight  lines.  This  detail  we  believe  to  be  quite 
novel  and  to  overcome,  in  a  great  degree,  the  objections  which 
have  heretofore  been  raised  concerning  derrick  bridges. 

The  calculations  of  strains  and  computations  of  quantities 
are  correct,  but  there  are  some  deficiencies  in  the  wind  bracing 
between  the  two  principal  trusses,  which  would  somewhat  in- 
crease the  quantities  of  material  estimated.  The  most  objec- 
tionable feature  about  the  design,  however,  is  the  fact  that  both 
the  roadway  and  the  sidewalks  are  placed  upon  projecting 
brackets  outside  of  the  line  of  the  trusses,  the  brackets  being 
imperfectly  connected  to  the  boom,  thus  giving  a  narrow  base 
and  objectionable  arrangement.  The  plan,  nevertheless,  is  a 
good  one,  but  not  the  most  economical  one.  It  is  estimated  to 
cost  $2,610,785  for  a  double  track  throughout,  the  designer  not 
having  furnished  a  plan  for  a  single  track  bridge  susceptible  of 
future  enlargement. 

The  greater  cost  of  Messrs.  Flad  &  Co.'s  design  is  probably 
due  to  the  fact  that,  as  each  set  of  straight  suspension  links  sup- 
port a  uniform  length  of  50  feet,  they  have  to  provide  for  the 
maximum  live  load  which  occurs  upon  such  a  span,  say  4,750 
pounds  per  lineal  foot,  while  the  maximum  weight  which  can 


16 


come  upon  the  whole  of  the  734  feet  aggregating  these  spans 
averages  only  3,370  pounds  per  lineal  foot. 

It  is  but  just  to  mention,  in  this  connection,  that  two  meritori- 
ous designs  for  double  track  railway  and  roadway  bridges,  on 
the  derrick  plan,  were  originally  submitted  to  your  Company 
by  Professor  W.  P.  Trowbridge  of  New  Haven.  We  regret 
that  his  many  engagements  did  not  admit  of  his  revising  them 
to  conform  to  our  specifications,  especially  as  Professor  Trow- 
bridge was  one  of  the  earliest  to  interest  himself  in  the  project 
for  a  bridge  at  Blackwell's  Island  and  to  propose  a  derrick  plan 
therefor.  We  have  received  from  him  a  communication  and 
-estimate  concerning  the  cost  of  a  tunnel  at  the  location  pro- 
posed for  your  bridge,  which  we  submit  to  your  Board  here- 
with. 

But  few  of  the  seven  plans  which  have  thus  far  been  dis- 
cussed are  accompanied  with  direct  tenders  from  bridge  firms 
for  their  construction.  Some  of  the  estimates  of  cost,  therefore, 
may  require  revision  as  to  prices,  as  well  as  to  quantities  of 
materials  needed  to  supply  deficiencies. 

The  two  plans  which  remain  to  be  described,  however,  are 
not  only  the  best  in  themselves,  as  we  are  all  agreed,  but  are 
backed  by  responsible  bridge  contractors  of  high  standing,  who, 
as  we  understand,  are  prepared  to  enter  into  contracts  for  their 
construction  at  the  specified  sums. 

Either  of  the  designs  is  a  proper  one  to  be  adopted  and 
erected ;  and,  with  such  modifications  and  improvements  as 
the  builders  would  doubtless  wish  themselves  to  make  in  pre- 
paring their  final  plans,  is  likely  to  give  good  satisfaction. 

VIII,  The  firm  of  Clarke,  Reeves  &  Co.,  of  the  Phoenixville 
Bridge  Works,  submit  a  design  in  which  they  propose  to  erect 
for  the  spans  across  the  river  the  plan  of  hinged  arch  invented 
and  patented  by  Capt.  James  B.  Eads,  the  distinguished  engineer 
of  the  St.  Louis  Bridge. 

A  side  view  is  shown  on  plate  VIII. 

The  arch  proper  consists  of  two  Lenticular  struts  or  girders 
resting  against  each  other  in  the  centre,  where  they  are  hinged, 
and  also  hinged  at  the  top  of  the  piers.  To  sustain  these  hinge 
points,  struts,  made  like  the  girders,  continue  the  arch  form  to 
abutments  on  the  rock  foundation  below. 


< 
- 


17 


The  main  arches,  or  top  members,  are  to  be  of  "  Phoenix  '  ' 
columns  of  wrought  iron,  30  inches  in  external  diameter,  put 
together  in  straight  pieces,  each  one  panel  in  length,  except 
where  the  openings  for  rail  and  roadways  occur.  At  these  they 
will  be  at  least  two  panels  in  length,  and  the  adjoining  joints  in 
the  contiguous  columns  will  be  likewise  additionally  strength- 
ened. 

The  lower  members,  or  counter  arches,  are  made  of  plates 
and  angles,  riveted  together  so  as  to  form  channel  beams.  The 
web  members  are  10  inch  channel  bars,  attached  to  the  upper 
and  lower  arches  by  pin  connections.  These  form  between  the 
piers  two  semi-arches  or  "  lunettes,"  the  thrusts  of  which  are 
mainly  carried  to  the  foundation  by  the  braced  continuation  or 
arched  strut  already  mentioned. 

The  piers,  which  are  composed  of  Phoenix  columns,  and 
braced  both  transversely  and  diagonally,  are  designed  to  take 
only  such  strains  as  may  come  upon  them  from  unequal  load- 
ing of  the  arches  and  a  portion  of  the  strain  from  wind  pressure. 
These  strains  are  alternately  compressive  and  tensile,  and  the 
piers  are  therefore  designed  to  resist  compression  as  well  as 
tension,  and  to  be  anchored  to  their  foundations. 

The  floor  system  consists  of  iron  cross-floor  beams  two  feet 
deep,  made  of  plates  and  angle  irons,  and  of  longitudinal  string- 
ers fifteen  inches  deep.  The  cross-floor  beams  are  suspended 
from  the  arch  by  flat  bars  of  varying  length  latticed  together, 
the  longest  suspender  being  at  the  centre,  and  eighty  feet  lon^. 
The  floor  is  divided  by  four  ribs  or  arches  into  three  roadways 
of  equal  width,  the  central  one  being  occupied  by  the  railroad 
and  the  outer  ones  by  the  roadways  and  sidewalks.  This  is  a 
convenient  arrangement  for  a  single  track  road,  but  if  a  second 
track  is  to  be  hereafter  added,  provision  must  be  made  for  it 
now  by  building  the  outer  arch  strong  enough  to  carry  the  in- 
creased load  hereafter  to  be  thrown  upon  it.  The  cost  of  this 
is  estimated  by  the  designers  at  $151,000.  The  total  width  of 
the  structure  is  fifty-seven  feet  from  out  to  out,  thus  affording 
good  opportunity  for  lateral  bracing. 

As  was  to  be  expected  from  the  known  experience  and  abil- 
ity of  this  firm,  the  plans  are  very  thoroughly  and  carefully 
worked  out  in  all  their  details  ;  the  strain  sheets,  calculations 
and  computations,  so  far  as  submitted,  are  found  to  be  correct, 


18 


and  the  design  not  only  possesses  great  merits  intrinsically,  but 
has  been  so  nearly  perfected  as  to  leave  but  little  room  for  im- 
provement. 

It  may  be  objected  that  it  does  not  leave  throughout  its  entire 
length  an  unobstructed  head  room  of  the  full  height  required  by 
the  charter  for  the  middle  of  the  river  (130  feet).  In  the  plan 
presented  the  lowest  part  of  the  bridge  is  135  feet  above  mean 
high  tide  at  the  middle  ;  at  a  distance  of  200  feet  from  the  cen- 
tre it  is  130  1-10  feet ;  at  the  shores  it  is  108  feet.  The  arrange- 
ment is  stated  by  the  firm  not  to  be  indispensable  to  the  success 
of  the  design,  and  that  the  arches  can  be  raised  if  thought  to 
obstruct  navigation.  In  accordance  with  this  last  suggestion  a 
modified  design  has  been  prepared  and  sent  to  us,  on  which 
the  clear  height  at  the  shores  is  120  feet,  or  the  same  as  for  the 
Brooklyn  Bridge.  This  change  is  stated  to  require  no  modifi- 
cation in  the  estimates. 

This  plan  of  a  hinged  arch  would  be  an  admirable  one  for 
a  deep  sunken  stream,  with  precipitous  rocky  sides,  as  at  the 
Niagara  Suspension  Bridge.  The  topography  of  such  a  loca- 
tion, and  the  absence  of  all  navigation,  would  also  greatly  facili- 
tate and  cheapen  its  erection  ;  for,  in  a  span  of  700  or  800  feet, 
one  of  the  chief  problems  to  be  solved  is,  how  to  get  it  into 
place  without  inadmissible  expense  and  without  danger  of 
wreck  during  its  construction. 

Messrs.  Clarke,  Reeves  &  Co.  propose  to  adopt  a  method 
somewhat  similar  to  that  employed  at  the  St.  Louis  Bridge,  and 
to  project  each  semi-arch,  panel  by  panel,  from  the  shore,  sus- 
pending it,  as  it  progresses,  from  a  series  of  inclined  stays 
fastened  to  temporary  towers  at  the  piers,  and  anchored  back  to 
the  shores.  Each  semi-arch  would  thus  project  beyond  the 
stays  until  both  meet  in  the  centre  of  the  river,  where  the  cen- 
tral hinge  could  be  inserted,  and  the  weight  taken  oft'  from  the 
stays.  This  method  proved  successful  at  St.  Louis  for  spans  of 
515  feet.  Whether  it  could  as  successfully  be  applied  to  this 
one  of  749  feet  admits,  perhaps,  of  some  question,  as  the 
weights  to  be  controlled  are  larger,  and  their  leverage  greater, 
while  the  circumstances  of  the  case  are  somewhat  different. 

Although  the  erection  would,  at  first  sight,  appear  to  be  diffi- 
cult, expensive,  and  perhaps  hazardous,  we  are  informed  by  the 
projectors  that  they  have  convinced  themselves  of  its  entire 


L9 


practicability,  and  provided  for  it  in  the  estimates  by  careful 
calculations  of  the  cost  of  erection. 

In  view  of  the  high  character  and  known  skill  of  these  gen- 
tlemen, therefore,  we  do  not  feel  authorized  to  dwell  upon  this 
point  further. 

In  consequence  of  an  ambiguity  in  our  specifications,  as  to 
whether  the  formula  given  for  calculating  the  strains  upon  com- 
pression members  applied  to  sections  shorter  than  24  radii  of 
gyration,  the  designers  (construing  the  clause  strictly  against 
themselves)  have  calculated  the  strains  upon  the  main  arches  at 
8,000  pounds  to  the  square  inch  of  section,  and  thus  provided  for 
a  structure  materially  stronger  than  would  have  resulted  from 
the  alternative  construction  of  the  clause  (as  adopted  by  the  other 
designers),  which  gives  as  a  result  in  some  cases  about  11,000 
pounds  to  the  square  inch,  and  would  have  saved  some  900,000 
pounds  of  material  in  the  largest  span  alone  in  this  design. 

We  are  informed  by  Messrs.  Clarke,  Reeves  &  Co.  that 
1,100,000  lbs.  of  iron,  included  in  their  estimate  of  weights,  is 
wholly  required  in  the  erection  of  the  bridge.  This  amount  of 
iron  should  therefore  be  deducted  from  the  actual  weight  of  the 
completed  structure.  The  large  amount  estimated  for  raising 
the  arches  may  be  taken  as  an  evidence  of  the  regard  to  safety 
in  designing  the  means  of  erection. 

Objections  might  perhaps  be  taken  to  the  necessity  of  sus- 
pending the  floor  from  the  panel  points  of  the  arch,  but  the 
designers  have  judiciously  planned  to  lattice  together  the  sus- 
pension ties  (the  longest  of  which  is  eighty  feet  long)  in  order 
to  give  the  floor  platform  lateral  stability  and  counteract  the 
tendency  to  swing  sideways  from  the  effect  of  the  wind. 

We  may  notice  the  following  points  which  would  require 
attention,  were  the  plan  to  be  selected  for  erection  : 

1.  The  lateral  bracing  is  necessarily  omitted  out  of  eight 
panels  in  the  counter  arch  and  four  panels  in  the  main  arch,  in 
order  to  allow  for  head  room  in  the  roadway  where  its  line  in- 
tersects that  of  the  arches.  This  would  require  the  strengthen- 
ing of  the  joints  and  columns  past  these  points. 

2.  The  piers  being  designed  mainly  to  form,  with  the  in- 
clined struts,  fixed  points  for  the  hinges  of  the  lunettes,  and 
bearing  none  of  the  dead  load,  cannot  form  supports  against 
strains  from  the  live  load,  arising  from  partial  loading,  without 


20 


being  anchored  down  to  the  foundation  ;  and  this  feature  seems, 
therefore,  inherent  in  the  design. 

3.  Changes  of  temperature  will  tend  to  move  the  tops  of  the 
piers  in  the  line  of  the  axis  of  the  bridge.  This  motion,  how- 
ever, will  amount  to  but  \  %  inches  for  the  whole  range  of  150 
degrees  provided  for  by  the  specification,  and  the  piers  may 
bend  so  much  without  danger. 

As  a  whole,  the  design  provides  for  a  structure  of  great  merit. 
The  cost  for  a  single  track  throughout,  without  the  tunnel,  is 
estimated  at  $1,767,274.  For  double  track  approaches  on  the 
New  York  and  Long  Island  sides,  and  single  track  across  both 
arms  of  the  river  and  across  BlackwelPs  Island,  it  is  $1,932,878. 
If,  however,  it  is  desired  to  provide  for  an  eventual  second 
track,  the  cost  of  first  erection  will  be  increased  by  $151,000, 
say  to  $2,083,878,  while  the  addition  of  the  second  track  (at 
present  prices)  would  cost  $202,400  more  ;  thus  making  the 
cost  of  a  double  track  structure  throughout  $2,286,278. 

IX.  The  plans  presented  by  Mr.  Charles  Macdonald  for  the 
Delaware  Bridge  Company  propose,  for  the  spans  across  the 
East  River,  a  novel  modification  of  the  Cantilever  type  of 
bridges. 

This  type  has  hitherto  been  planned  with  only  two  chords  or 
booms,  placed  as  far  apart  vertically  as  proved  most  economical 
for  the  intermediate  connecting  web.  This  arrangement  is  the 
existing  and  correct  practice  for  girder  or  truss  bridges,  and 
insures  economy  of  material,  by  carrying  the  strains  as  far  from 
the  neutral  axis  as  possible. 

In  a  Cantilever  bridge,  however,  the  two  Cantilevers,  bal- 
anced over  each  pier,  form  brackets,  the  shore  ends  of  which  are 
anchored  down,  and  their  outer  ends  sustain  a  central  span, 
merely  resting  upon  them,  and  free  to  expand  and  contract  with 
changes  of  temperature. 

These  brackets,  therefore,  perform  a  double  function.  They 
sustain  their  own  weight  and  their  proper  rolling  load  to  the 
extremity  of  their  arms,  and  they  also  sustain  the  weight  of  the 
central  span  and  its  proper  rolling  load,  extending  between 
the  ends  of  the  brackets. 

The  Delaware  Bridge  Company  propose  to  avail  of  this 
division  of  functions,  by  sub-dividing  the  Cantilever  vertically 


21 


into  three  brackets,  superposed  to  each  other  by  means  of  inter- 
mediate chords  as  shown  on  plate  IX. 

The  designer  claims  that,  by  this  arrangement,  the  weight  is 
kept  as  low  as  possible,  and  that  by  avoiding  the  necessity  for 
carrying  all  the  weight  to  the  top  of  the  central  tower  over  the 
pier,  there  results  not  only  great  economy  in  this  tower,  but 
also  in  all  the  compression  members  of  the  web,  which  become 
of  the  simplest  form  and  most  manageable  lengths,  while  the 
stability  is  greatly  increased,  and  the  erection  becomes  so  sim- 
ple and  cheap  that  the  structure  furnishes  its  own  false  works 
except  for  the  central  space. 

Each  Cantilever,  or  bracket,  is  divided  by  the  two  interme- 
diate chords  into  three  subsidiary  brackets  superposed  to  each 
other,  and  36  feet  deep.  These  again  are  divided  vertically  into 
panels  30  feet  long  by  the  posts,  those  posts  alone  carrying  the 
live  and  dead  load,  to  which  the  diagonal  ties  are  attached ; 
the  posts  above  these  merely  serving  to  carry  the  weight  of  the 
Cantilever  chords,  and  to  prevent  them  from  sagging  below  a 
straight  line. 

The  process  of  erection  consists  in  extending  the  parts  with  a 
balanced  beam,  panel  by  panel,  each  side  of  the  pier,  using  each 
subsidiary  bracket  as  the  foundation  for  that  overlying  it,  and 
then,  after  the  brackets  are  completed,  rolling  a  counterbalanced 
wooden  truss,  300  feet  long,  into  the  intervening  space,  on  and 
around  which  to  erect  the  central  span,  which  is  200  feet  in 
length. 

The  shore  ends  of  the  Cantilevers  are  sustained  by  three  piers, 
through  which  the  anchorage  is  distributed. 

There  are  three  trusses,  the  bridge  being  divided  by  them  in 
cross  section  into  two  roadways,  one  for  the  railroad,  and  the 
other  for  a  double  carriage  roadway  20  feet  wide  ;  the  sidewalks 
being  placed  on  brackets  overhead  of  the  carriage  roadway. 
When  a  second  track  is  to  be  added,  it  is  to  be  provided  for  by 
independent  trusses  on  the  other  side  of  the  carriage  roadway, 
which  would  then  be  in  the  middle. 

The  lower  boom,  or  chord,  is  composed  of  24-inch  iron 
plates  and  8-inch  channel  bars,  riveted  together  into  the  form 
of  a  continuous  box  girder  open  at  the  top.  The  vertical  posts 
consist  of  two  channel  bars  each,  latticed,  and  the  diagonals  and 
the  suspension  chains,  or  upper  chords,  are  of  flat  bars,  6  inches 


22 


wide.  All  the  verticals,  diagonals  and  suspension  chains,  or 
chords,  are  connected  with  each  other  and  with  the  lower  chord 
and  towers  by  pin  joints.  The  towers  are  composed  of  posts 
made  of  plates  and  channel  bars,  latticed,  and  are  braced  both 
transversely  and  diagonally. 

The  shore  piers,  on  which  the  arms  of  the  Cantilever  rest, 
are  similar  to  the  towers,  and  anchored  to  the  foundation  so  as 
to  resist  both  compression  and  tension. 

The  floor  consists  of  iron  cross-floor  beams,  made  of  plates 
and  angle  irons  and  of  longitudinal  iron  stringers,  braced  by 
diagonal  lateral  rods.  The  main  cross-floor  beams  are  sus- 
pended from  the  pins  at  each  panel  point. 

The  sidewalks  are  carried  on  brackets  fastened  to  the  ver- 
tical posts  above  the  main  floor.  The  central  span  is  a  Pratt 
truss,  with  pin  connections,  and  a  double  system  of  diagonals. 
The  posts  and  upper  chords  are  made  of  plates  and  channel 
bars,  and  the  tie  rods  and  lower  chords  of  flat  bar  links  as  in 
ordinary  spans  of  that  class.  This  span  merely  rests  upon  the 
outer  ends  of  the  arms  of  the  two  Cantilevers,  one  end  being 
provided  with  rollers  to  allow  of  expansion  and  contraction. 

Not  only  is  the  structure  rigid,  economical  and  capable  of 
erection  with  great  ease  and  without  danger  of  disaster  or  inter- 
ference with  the  navigation,  but  it  seems  to  us  capable  of  still 
further  improvement  by  revising  the  general  proportions,  the 
most  economical  arrangement  of  which,  it  may  well  be,  the  de- 
signer has  not  attained  in  so  novel  a  plan. 

The  sections  of  the  compression  members  have  been  calcu- 
lated by  the  formula  given  in  the  specifications  for  parts  exceed- 
ing twenty-four  radii  of  gyration,  which  results  in  strains  of 
about  9,000  pounds  per  square  inch,  and  some  of  these  mem- 
bers, therefore,  have  relatively  less  section  than  the  correspond- 
ing parts  in  the  design  of  Clarke,  Reeves  &  Co. 

Some  of  the  wind  strains  are  also  deficient  in  consequence  of 
an  under  estimate  of  the  developed  surface  exposed  by  some  of 
the  parts. 

In  addition  to  this  we  may  call  attention  to  the  following 
minor  deficiencies : 

1.  There  is  no  provision  made  for  carrying  the  wind  strains 
past  the  openings  in  the  central  towers  through  which  the  road- 
ways run.    This  can  readily  be  overcome  by  suitable  portals. 


23 


2.  The  foundation  of  the  main  towers  is  not  spread  sufficiently 
wide  to  overcome  the  overturning  tendency  from  wind  strains. 
In  order  to  avoid  the  consequent  necessity  for  anchoring  the 
posts  down  to  their  foundation,  which  is  an  objectionable 
arrangement,  it  would  be  advisable  either  to  spread  the  base  of 
the  towers,  or  to  design  the  bridge  with  only  two  trusses  instead 
of  three,  so  as  to  concentrate  all  the  weight  upon  the  outside 
posts. 

3.  The  effect  of  the  live  load,  when  only  one  arm  of  the 
Cantilever  is  loaded,  will  be  to  produce  a  bending  strain  in 
the  towers  and  to  throw  the  weight  upon  one  set  of  tower 
posts  instead  of  distributing  it  over  the  whole.  This  requires 
some  changes  in  the  connection  of  the  chords  or  chains  with 
the  tops  of  the  towers,  so  that  the  weights  may  be  transmitted 
without  producing  a  bending  strain. 

The  cost  for  a  single  track  throughout,  without  the  tunnel,  is 
estimated  at  $1,778,315.  For  double-tracked  approaches  on 
the  New  York  and  on  the  Long  Island  sides,  and  single  track 
across  both  arms  of  the  river  and  Blackwell's  Island,  the  cost 
will  be  $2,031,425,  while  for  a  double  track  structure  through- 
out it  will  be  $2,479,458  ;  and  the  Delaware  Bridge  Company 
makes  a  formal  tender  to  take  the  contract  at  these  prices, 

NON-COMPETING  PLANS. 

During  the  last  week  in  January  the  Passaic  Rolling  Mill 
Company  brought  in  a  set  of  plans  and  a  tender  for  the  con- 
struction of  your  bridge,  which  other  engagements  had  pre- 
vented that  Company  from  completing  sooner. 

These  we  could  not  in  fairness  consider  with  the  other  de- 
signs handed  in  at  the  specified  time  in  competition  for  the  pre- 
miums offered,  nor  was  it  expected  that  we  should  ;  the  parties 
who  had  been  at  the  trouble  and  expense  of  finishing  them  sub- 
mitting the  plans  mainly  as  the  evidence  of  their  being  pre- 
pared to  undertake  such  works. 

These  plans,  which  were  prepared  by  Mr.  C.  O.  Brown  for 
the  Passaic  Rolling  Mill  Company,  are  sound  and  good.  They 
provide  for  a  Cantilever  bridge,  the  main  feature  of  which  is 
the  long  central  span  of  330  feet.    It  is  shown  on  plate  X. 


24 


So  far  as  we  have  been  enabled  to  check  them  over,  the  com- 
putations of  strains  and  quantities  are  correct.  The  estimate  of 
cost  however,  is  somewhat  higher  than  for  the  plans  of  Messrs. 
Clarke,  Reeves  &  Co.  or  the  Delaware  Bridge  Company,  being 
$1,885  000  f°r  a  single  track  structure,  without  the  tunnel,  or 
$1,985,000  including  the  tunnel;  at  which  price  the  parties 
made  a  formal  tender  for  the  whole  work. 

We  regret  that  Mr.  Charles  Bender,  who  originally  made  a 
valuable  preliminary  report  to  your  Board  of  Directors  and 
presented  plans  for  a  Cantilever  bridge  possessing  great  merit, 
did  not  find  himself  at  leisure  to  revise  those  plans  and  estim- 
ates of  cost,  in  order  to  make  them  conform  to  our  specifica- 
tions, so  that  we  might  consider  them  in  competition  with  the 
others.  Mr.  Bender  was  among  the  first  to  take  an  interest  in 
your  enterprise  and  to  make  valuable  suggestions  about  its  con- 
struction, by  which  all  designers  have  probably  profited  ;  while 
his  original  plan  contained  such  excellent  features  that  we  should 
probably  have  had  the  satisfaction  of  recommending  it  among 
the  best,  had  it  been  made  to  conform  to  the  terms  of  the  circu- 
lar inviting  designs. 

We  also  regret  that  the  Baltimore  Bridge  Company,  which 
had  originally  sent  in  a  preliminary  study  for  a  counter-balanced 
Cantilever  span,  was  unable,  from  press  of  other  engagements, 
to  complete  the  plans  which  we  understand  them  to  have  begun. 
We  would  have  been  quite  certain  to  receive  good  plans  from 
this  skillful  and  experienced  firm.  . 

GENERAL  FEATURES. 

Whether  the  structure  shall  be  for  a  single  or  double  railway 
track  depends  upon  the  estimates  of  its  future  business.  We 
would  recommend  that  the  tunnel  and  the  approaches,  on  both 
the  New  York  and  Long  Island  sides,  be  built  for  double  track, 
and  that  the  main  spans  and  trestle  across  Blackwell's  Island 
should  be  for  single  track,  with  provision  for  an  eventual  second 
track,  if  required.  For  these  elements  the  bridge  proper  will 
cost,  according  to  the  estimates  of  Clarke,  Reeves  &  Co., 
$2,083,875  ;  and  according  to  those  of  the  Delaware  Bridge 
Company,  $2,031,425.    The  tunnel  will  probably  cost  about 


25 


$200,000  more,  and.  if  the  office  expenses  and  engineering  be 
estimated  at  from  $116,122  to  $168,575  morei  the  total  cost  of 
your  enterprise  will  be  $2,400,000,  exclusive  of  the  right  of  way. 
If  built  for  a  single  track  throughout,  the  cost  will  not  exceed 
$2,100,000,  exclusive  of  the  right  of  way. 

ORDER  OF  MERIT. 

Having  now  completed  our  general  review  of  the  competing 
plans,  it  only  remains  for  us  to  advise  vou  as  to  which  we  deem 
the  three  "  best "  designs  and  to  indicate  the  relative  rank,  in 
our  estimation,  of  these  three. 

In  this  connection  we  quote  the  resolution  of  the  Board  of 
Directors  of  August  9,  1876  : 

Resolved,  That  the  time  for  receiving  plans  be  extended  to  December  1,  1876, 
and  that  the  Engineers  give  notice,  with  a  view  of  bringing  out  the  best  talent  in 
the  country,  that  this  Companv  will  pay  to  the  party  whose  plan  shall  be  adopted 
as  the  best  the  sum  of  one  thousand  dollars  ;  for  the  second  best,  five  hundred 
dollars,  and  for  the  third,  two  hundred  and  fifty  dollars.  Plans  so  paid  for  to  be 
the  property  of  the  Company.  The  awards  to  be  made  by  this  Board  under  ad- 
visement of  the  consulting  engineers. 

Our  estimate  of  relative  merits  will  be  best  rendered  by  the 
following  transcript  of  minutes  of  proceedings  of  the  commis- 
sion of  consulting  engineers  on  the  evening  of  February  5,  1877  : 

"The  individual  opinions  of  the  members  of  your  consulting  engineers  upon 
the  order,  each  being  taken  absolutely  without  modifications,  and  as  entirely  with 
reference  to  its  strain  sheets  and  specifications,  are  as  follows  : 

(  Best — Delaware  Bridge  Company* 
O.  CHANUTE,        \  Second—  Clarke,  Reeves  &  Co. 

(  Third — Flad  &  Co. 

I  Best — Clarke,  Reeves  &  Co. 
J.  G.  BARNARD,    I  Second — Delaware  Bridge  Comp'y. 
(  Third — Flad  &  Co. 

I  Best — Clarke.  Reeves  &  Co. 
Q.  A.  GILLMORE,  -  Second — Delaware  Bridge  Comp'y. 

I  Third — Edward  Serrell  &  Sox. 

Taken,  however,  as  a  whole  upon  the  general  question,  as  to 
which  plan  we  would  recommend  to  be  adopted  for  practical 


26 


construction  by  your  Company,  with  such  improvements  and 
modifications  as  suggest  themselves,  the  order  of  our  preference 
would  be  as  follows  : 

i  Best — Delaware  Bridge  Company. 
O.  CHANUTE.        <  Second—  Clarke,  Reeves  &  Co. 

'  Third—  Flad  &  Co. 

i  Best — Clarke,  Reeves  &  Co. 
J.  G.  BARNARD,    ■  Second — Delaware  Bridge  Comp'y. 
(  T/u'rd—FL\D  &  Co. 

i  Best — Delaware  Bridge  Company. 
Q.  A.  GILLMORE,  <  Second—  Clarke,  Reeves  &  Co, 
(  Third — Edward  Serrell  &  Son. 

From  the  foregoing  it  will  appear  that,  while  there  is  entire 
unanimity  as  to  the  two  best  plans  which  we  advise  for  award, 
the  same  is  not  found  as  to  the  order  of  merit  of  these  two. 

Two  out  of  the  three  pronounce  the  plan  of  Clarke,  Reeves 
&  Co.  the  best,  if  taken  absolutely  without  modification,  and 
entirely  with  reference  to  its  strain  sheets  and  specifications. 

While  two  out  of  three  pronounce  the  Delaware  Bridge 
Company's  plan  "  best "  to  recommend  to  be  adopted  for  prac- 
tical construction  by  your  Company,  with  such  improvements 
and  modifications  as  suggest  themselves. 

With  regard  to  the  "  third  k  best ',"  two  out  of  three  agree  in 
giving  the  award,  on  both  the  grounds  on  which  the  votes  were 
taken,  to  Flad  &  Co.  One,  Gen.  Gillmore,  considered,  under 
both  points  of  view,  the  plan  of  Edward  Serrell  &  Son  as  en- 
titled to  that  rank. 

Submitting  the  foregoing  as  the  result  of  their  united  action, 
the  individual  members  will,  to  the  extent  they  see  fit,  set  forth 
their  reasons  for  their  individual  preferences. 

Respectfully  submitted, 

O.  CHANUTE, 
J.  G.  BARNARD, 
Q.  A.  GILLMORE. 


27 


SUPPLEMENTARY  REPORT  OF  GEN.  BARNARD. 


New  York,  February  21,  1877. 

To  the  President  and  Directors  of  the  New  York  and  Long 
Island  Bridge  Company  : 

Gentlemen  : — 

The  concluding  paragraph  of  the  joint  report  of  the  Board  of 
Consulting  Engineers  to  your  honorable  body  of  this  date,  closes 
with  the  statement :  "  The  individual  members  will,  to  the  ex- 
tent they  see  fit,  set  forth  their  reasons  for  their  individual  pre- 
ferences." As  my  own  views  on  the  subject  of  two  of  the  com- 
peting plans  would  be  incompletely  expressed  without  such  an 
exposition,  I  herewith  present  the  statement  therein  contem- 
plated. 

I  am  very  respectfully, 

Your  most  obedient, 

J.  G.  BARNARD, 
A I  ember  of  the  Board  of  Consulting  Engineers. 


The  undersigned,  a  consulting  engineer,  to  select  the  best 
plan  for  your  proposed  bridge,  and  to  advise  as  to  the  awards 
to  be  made  by  your  Board  for  "  best,"  "  second  best "  and 
"  third  best "  plans,  having  recorded  his  opinion,  that,  whether 
considered  uabsolutelyswithout  modification,"  or  as  a  "plan  to  be 
adopted  for  practical  construction  by  your  company,  with  such 
improvements  and  modifications   as  suggest  themselves,"  the 


28 


plan  of  "Clark,  Reeves  &  Co."  is  entitled  to  the  award  of  "best," 
briefly  submits  the  following  reasons  for  his  preference  : 

I. —  Simplicity  of  design. 

In  this  respect  it  is  unrivalled.  The  arch  is  recognized  as 
theoretically  the  form  for  bearing  compressively  a  permanent 
load — the  parabola,  its  proper  trace,  when  the  load  is  uniform. 
The  combination  in  this  bridge,  while  giving  the  arch  as  the 
permanent  load-bearer,  breaks  it  at  the  crown  and  skewbacks 
(by  hinges)  to  avoid  temperature  strains.  In  this  point  of  view 
the  principle  is  again  the  most  simple  and  elementary  in  bridge 
building — the  juxtaposition  from  the  opposite  banks  (when  the 
span  becomes  too  great  for  a  single  beam)  of  two  struts  meet- 
ing at  an  angle  in  the  middle. 

In  short  spans,  where  this  simple  triangle  of  parts  first  finds 
its  application,  the  thrust  is  usually  taken  by  a  tie  or  chord. 
For»large  spans,  if  a  tie  be  used,  the  deflection  due  to  load  is 
thereby  doubled,  since  the  tie  is  stretched  as  much  as  the  arch 
member  is  compressed. 

Hence  the  advantage  claimed  in  this  design  of  carrying  the 
thrust  direct  to  the  ground  by  a  short  compression  member  (a 
continuation  of  the  arch  form)  reaching  from  the  abutment 
hinges  to  the  ground.  The  two  struts  into  which  the  arch  is 
divided  are  stiffened  each  by  a  counter-arch,  also  parabolic, 
giving  a  "lunette"  or  lenticular  form  to  these  members  almost 
exactly  corresponding  to  that  demanded  by  the  maximum  strains 
— a  correspondence  of  which  the  ordinary  "  girder"  (with  par- 
allel chords)  is  necessarily  destitute,  and  for  which  the  gradua- 
tion of  weight  of  metal  in  its  parts  is  the  imperfect  substitute. 

The  resulting  external  form,  an  arch  springing  from  the  very 
shores,  gives  to  the  structure  a  singular  beauty  ;  a  point  by  no 
means  to  be  disregarded.  It  should  be  further  stated  in  this 
connection,  that  while  the  design  is  called  an  invention,  the 
word  refers  exclusively  to  the  combination  by  which,  for  spans 
of  extraordinary  length,  the  same  simple  elements  are  made 
available  as  those  which  for  ages  have  been  in  common  use  for 
the  shortest.  In  this  point  of  view  there  is  nothing  whatever 
"  experimental,"  the  action  of  every  part  is  well  known  by  ex- 
perience. 


29 


The  u  cantilever  "  principle  is  far  more  open  to  the  charge  of 
being  untried  or  "  experimental."  In  endeavoring  to  cite  a 
precedent  for  such  a  bridge,  Mr.  Bender  *  is  driven  to  the  irrele- 
vant structure,  a  "  cantilever  bridge  with  two  arms,"  as  he  calls 
it,  the  Brest  drawbridge,  consisting  of  two  balanced  swinging 
arms,  the  longer  members  of  which,  together,  span  a  clear 
interval  of  354  feet.  This  is  no  railroad  bridge.  A  narrow 
carriage-way  with  sidewalks  alone  occupies  it,  and  no  long 
independent  truss  fills  a  vacuum  in  the  middle  and  hangs  with- 
out connection,  almost,  with  its  total  dead  and  live  load,  on  the 
extreme  ends  of  the  so-called  "  cantilevers."  On  the  contrary, 
these  members  of  the  Brest  bridge  k'  are  wedged  together  in  the 
centre  so  as  to  act  partly  as  an  arch,  when  the  load  comes  upon 
it."  The  numerous  wooden  and  cast-iron  bridges  in  Holland, 
England,  Germany,  etc.,  also  cited,  are  too  insignificant,  or  too 
irrelevant  to  be  referred  to  as  furnishing  any  experimental  basis 
for  great  span  cantilevers ;  the  great  variety  of  designs  for 
which  are  sufficient  proofs  that  there  is  no  such  basis. 

II.  — Perfect,  or  almost  perfect,  eli?nination  of  temperature 

strains. 

This — one  of  the  difficulties  of  long  span  bridge  construction 
— is  accomplished  by  the  hinges  at  the  crown  and  at  the  abut- 
ment, by  hingeing  the  suspended  floor  at  its  middle  point,  and 
by  allowing  play  for  variations  of  length  at  its  connection  with 
the  counter-arches. 

The  slight  temperature  strain  thrown  upon  the  pier  by  the 
abutment  strut — easily  calculated — may  be  disregarded.  This, 
too,  might  be  completely  eliminated  if  it  were  worth  while. 

III.  — Perfect  deter minateness  of  strains,  ?zot  only  in  the  nor- 

mal configuration,  but  when  under  the  slight  distortions 
produced  by  partially  distributed  '*  live  "  loads. 

The  first  condition  flows  from  the  simplicity  of  design.  So 
also  does  the  latter  ;  but  it  is  by  no  means  inseparable  from  the 
first.  A  slight  distortion  of  the  piers  in  the  cantilever  may  very 
seriously  alter  the  actual  strains  from  those  of  calculated  strain 


*  "  Letter  to  your  Company,  September  20th,  1875.'' 


30 


sheets,  and  the  fact  is  strikingly  illustrated  in  the  competing 
cantilever  plan  for  which,  to  avoid  such  strains,  remodelling 
is  required.* 

IV.  — Perfect  fulfillment  of  the  requirements,  not  merely  of 

our  specifications"  which  leave  some  latitude  for  ar- 
rangement, but  of  convenience,  in  the  disposal  of  the 
thoroughfares. 

The  ample  width  of  57  feet,  from  outside  to  outside  of  exter- 
nal arches,  allows  to  be  centrally  placed  (as  it  should  be)  the 
railway  track,  while  the  two  outside  compartments  are  given 
up  to  exclusive  use  of  the  two  roadways,  each  with  its  sidewalk. 
The  breadth  of  base  which  allows  this  ample  room  for  the  thor- 
oughfares, is  also  an  important  element  in  the  stability  of  the 
bridge  against  wind  strains. 

V.  — Superiority  in  the  main  elements  which  constitute  the, 

structure,  and  fewness  of  parts. 

The  great  bearing  elements,  i.  e. :  the  main  "  arch  "  of  each 
"  lunette,"  or  half  strut,  the  abutment  strut  which  continues 
the  arch  form  to  the  ground,  and  the  columns  of  the  piers, 
etc.,  are  made  of  the  "Phoenix  columns,"  admittedly  the  best 
wrought  iron  "  post,"  or  compressive  member,  yet  designed, 
and,  in  my  opinion,  incomparably  preferable  to  the  latticed 
channel-iron  posts,  or  compressive  members,  we  find  in  all  the 
other  competing  designs.  The  Phoenix  columns  have  been 
found  experimentally  to  have  (see  Bender,  "Iron  Truss  Bridges 
in  America,"  p.  35)  an  ultimate  strength  far  higher  than  given 
by  Hodgkinson's  and  Gordon's  formulas,  by  which  it  is  usual 
(as  our  specifications  require)  to  determine  the  quantity  of  metal 
in  such  members.  These  members,  therefore,  thus  calculated, 
possess  an  excess  of  "  safety  "  beyond  our  safety  "  coefficients." 
But  not  only  do  they  possess  this  extra  strength,  but  they  have 
been  calculated  (according  to  the  specifications)  so  as  in  no 
case  to  receive  a  compressive  strain  of  more  than  8,000  pounds 
per  square  inch.  Under  the  formula  which  follows  this  specifi- 
cation, but  which  was  qualified  by  it,  for  compressive  members 


See  on  this  point  Mr.  Bender's  pamphlet,  11  Iron  Truss  Bridges  in  America,"  p.  24,  §2  . 


31 


longer  than  twenty-four  times  the  radius  of  gyration,  com- 
pressive strains  much  higher  have  been  taken  for  the  posts  of 
the  Delaware  Bridge  Company's  bridge.  This  accounts  for 
any  difference  there  may  appear  to  be  in  the  weight  per  foot 
in  favor  of  the  latter  bridge. 

To  this  superiority  of  form  and  fewness  of  parts  of  the  main 
elements  is  incidental  a  comparative  smallness  of  exposed  sur- 
face, which  is  hence  more  easily  and  inexpensively  protected 
from  corrosion. 

Nl.— Rigidity. 

In  this  important  feature — one  of  no  secondary  importance 
when  the  subjection  of  the  bridge  to  railway  trains  moving  at 
full  speed  is  considered — it  surpasses,  in  virtue  of  the  essential 
character  of  the  design  (alluded  to  under  I.  head)  all  others. 
A  reference  to  the  deflections  under  live  load  of  the  bridge  in 
question,  and  the  Delaware  Bridge  Company  illustrates  the  fact, 
for  the  former,  .30  of  a  foot  (in  the  centre)  ;  for  the  latter  .356 
(end  of  cantilever),  to  which  must  be  added  the  deflection  of 
the  200  foot  span  (.16  of  a  foot)  connecting  truss,  making  the 
total  .517  of  a  foot,  or  nearly  double  the  former.  The  Passaic 
Company's  cantilever  furnishes  about  the  same  result. 

VII. —  The  completeness  and  thoroughness  of  the  design  as  it 
is  actually  presented  for  your  consideration. 

No  "  modifications "  materially  affecting  the  design  as  now 
presented  have  been  suggested  and  none  are  required.  It  is 
not  pretended  by  the  designers  that  all  the  details  have  been 
worked  out ;  that  there  might  not  be,  with  improvement,  some 
changes  made.  But  what  is  maintained  here  is,  that  such 
requirements  refer  rather  to  filling  up  of  details  than  to  actual 
modifications. 

VIII. — Economy. 

As  this  is  determinable  from  the  estimate,  the  cost  is  about 
the  same  as  for  the  three  or  four  least  costly  competing  bridges, 
the  Delaware  Bridge  Company's  bridge  included. 

In  consideration  of  the  completeness  of  the  design  of  Clark, 
Reeves  &  Co.,  the  superiority  of  its  component  parts,  and  the 


32 


manner  in  which  its  weight  of  metal  has  been  calculated,  I  be- 
lieve it  to  be  much  the  least  expensive  bridge  of  any. 

Having  set  forth  what  I  consider  the  points — and  they  cover 
the  whole  field  of  inquiry — in  which  I  consider  the  Clark, 
Reeves  &  Co.'s  bridge  as  not  only  entitled  to  the  award  of 
"  best "  absolutely,  but  as  the  one  which  should  be  "  adopted 
for  practical  construction,"  I  shall  briefly  allude  to  the  objections 
offered  ;  and  first,  as  to 

I. — Anchorage. 

It  is  a  peculiarity  of  the  design  that  the  piers,  as  they  are 
called,  are  not  under  normal  conditions,  either  weight  or  thrust- 
bearing.  They  receive  the  strains  (whether  compression  or 
extension)  by  which  a  moving  load  would  tend  to  displace  the 
hinge-point,  and  they  receive,  in  a  large  degree,  wind  strains. 
The  mere  fact,  that  anchorage  is  necessary  to  meet  these  strains, 
is  no  more  an  objection  than  it  is  (where  equally  necessary) 
in  a  cantilever  or  suspension  bridge. 

II. —  The  want  of  provision  by  lateral  and  diagonal  bracing 
for  wind  strains  in  the  openings  for  the  roadways. 

It  is  not  believed  there  is  any  defect  here  which  can  not  be 
provided  for,  and  so  it  is  stated  in  the  main  report.  These  mat- 
ters are  not  exhibited  in  the  drawing.  The  designers  state  that 
they  have  been  fully  considered.  Something  equivalent  is  com- 
mon to  all  through  trusses,  and  a  nearer  resemblance  is  found 
in  the  St.  Louis  bridge.  The  cross  and  lateral  bracing  is  neces- 
sarily interrupted,  and  substitutes  for  these  members  is  found 
in  greatly  strengthening  the  main  members  and  in  a  proper 
application  of  braces  or  brackets. 

It  is  to  be  remembered  that  though  the  lunettes  rise  to  a 
height  at  point  of  meeting  of  80  feet  above  the  floor  (90  feet  in 
the  second  design),  the  point  of  attachment  of  the  floor  suspend- 
ers is  generally  comparatively  low,  rising  to  the  extreme  height 
only  through  a  short  interval  near  the  centre  of  the  bridge ; 
hence  the  floor  weight  (including  the  total  live  load)  is  not  in 
reality  borne  high. 


33 


III.  — An  objection  brought  against  the  design  (alluded  to  in  the 
joint  report)  is  that  a  large  portion  in  length  of  the  floor  is  sus- 
pended and  subject  by  the  wind  to  harmful  vibrations.  That 
the  measure  of  this  destructive  power  had  not  been  taken  in  earlier 
days  of  suspension  bridge  construction  is  notorious,  and  the  list 
of  English,  French  and  American  bridges  which  have  been 
injured  or  even  destroyed  would  be  great.  Even  the  Menai 
bridge  was  thus  injured  soon  after  it  was  built.  It  was  subse- 
quently re-inforced,  and  its  ordinary  roadway  and  foot  passen- 
ger floor,  5S0  feet  long  and  only  28  feet  wide,  weighing  but  950 
pounds  per  foot,  and  suspended  by  800  i-inch  square  iron  rods, 
varying  from  10  to  53  feet  in  length,  has  since  maintained  itself 
for  half  a  century.  The  long  half  spans  of  the  flooring  of  the 
Covington  and  Brooklyn  suspension  bridges,  800  feet  long  in 
the  latter  case,  present  greater  difficulties.  In  the  case  in  hand 
the  object  is  believed  to  be  fully  accomplished  by  the  horizontal 
"  wind  truss  "  underneath  the  floor,  having  57  feet  depth,  by  the 
rigid  (latticed)  suspenders,  and  by  their  overhead  cross-bracing. 
The  suspended  length  is,  in  one  design,  but  400,  in  the  other 
but  480  feet. 

IV.  — To  the  objection  of  difficulty  of  erection  I  was  at  first  dis- 
posed to  give  much  weight.  I  am  informed,  however,  by  the 
very  responsible  designers  that  the  matter  has  been  fully  con- 
sidered, the  cost  embraced  in  the  estimates,  and  that  they  are 
prepared  to  undertake  to  build  the  bridge  for  the  estimates. 

V.  — Finally,  I  will  allude  to  an  objection  much  insisted  upon, 
that  the  hinged  arch  design  does  not  lend  itself  to  furnishing  clear 
head-room  as  do  the  others.  The  second,  or  alternative  tracing, 
gives  the  same  head-room  throughout  as  the  East  River  Bridge 
gives  ;  indeed,  it  gives  more,  for  the  floor  holding-down  stays 
of  that  bridge  start  22  feet  below  the  floor  at  the  piers  and 
reach  out  nearly  200  feet,  reducing  the  120  feet  at  the  piers  to 
less  than  100  feet.  But  the  projectors,  in  submitting  their  de- 
signs, expressed  their  readiness  to  put  it  at  any  i-equired 
height.  I  do  not  think  any  raising  above  the  height  of  the 
second  tracing  at  all  necessary;  and,  at  the  same  time,  I  affirm 
that  there  is  no  bridge  proposed  to  us  so  capable  of  giving 
great  height  for  a  large  central  space — a  space  quite  wide 


34: 


enough  for  the  free  passage  of  all  large  vessels  (which  will 
avoid  close  approach  to  the  shores) — as  this  hinged  arch  design. 
You  have  simply  to  raise  the  Jloor  fifteen  feet  to  get  a  clear 
head  room  of  very  nearly  150  feet,  of  300  feet  width  on  the  first 
design  and  370  ieet  width  on  the  second. 

Respectfully  submitted, 

J.  G.  BARNARD, 
Member  of  Board  of  Consulting  Engineers. 


35 


SUPPLEMENTARY  REPORT  OF  GEN.  GILLMORE. 


New  Y ORK,  February  26,  1877. 

To  the  Directors,  Neiv  York  and  Long  Island  Bridge  Com- 
pany, New  York  City  : 

Gentlemen : 

In  the  report  of  your  Board  of  Consulting  Engineers  recently 
submitted,  I  am  on  record  as  having  expressed  my  preference 
for  the  three  best  plans  of  bridges  before  them,  in  the  following 
order,  upon  the  assumption  that  the  plans  are  to  be  considered 
strictly  with  reference  to  the  specifications  and  strain-sheets 
which  accompanied  them,  viz  : 

1.  The  design  of  Clarke,  Reeves  &  Co. 

2.  "  the  Delaware  Bridge  Company. 

3.  "         Edward  W.  Serrell  &  Son. 

With  certain  modifications  which  suggest  themselves,  and  of 
which  the  designs  are  susceptible,  without  resorting  to  any 
radical  change  in  the  character  of  the  structures,  my  preference 
was  expressed  in  the  following  order,  viz  : 

1.  The  design  of  the  Delaware  Bridge  Company. 

2.  "  Clarke,  Reeves  &  Co. 

3.  "  Edward  W.  Serrell  &  Son. 

It  seems  proper  that  I  should  state,  although  I  do  not  propose 
to  discuss  at  any  length,  the  grounds  upon  which  my  judgment 
in  the  matter  was  formed,  with  regard  to  the  two  first  named 
designs. 

The  design  of  Clarke,  Reeves  &  Co.  is  the  only  one  submitted 
to  us  that  I  would  be  willing  to  recommend  for  adoption  by 
your  company,  as  it  stands,  and  without  modification. 


36 


It  possesses,  in  my  judgment,  sufficient  strength  and  rigidity, 
while  any  tendency  to  overturn  bodily,  by  the  lateral  pressure  of 
high  winds,  appears  to  be  suitably  guarded  against  by  the  width 
of  the  bridge  (about  55  feet),  and  by  anchoring  the  towers  to 
their  foundations.  Inasmuch,  however,  as  both  the  centre  of 
gravity  and  the  centre  of  form  are  comparatively  high,  I  think 
the  towers  should  be  widened  10  to  12  feet,  by  spreading  them 
5  to  6  feet  on  either  side. 

I  apprehend  no  undue  or  dangerous  strains  from  the  tension 
in  the  towers,  caused  by  a  moving  load  upon  the  main  span,  as 
the  horizontal  thrust  would  be  amply  resisted  by  the  rigid  trian- 
gular system  at  each  of  the  shore  ends,  composed  of  the  towers 
themselves  and  the  lower  lenticular  trusses.  There  is,  however, 
an  inherent  local  weakness  against  wind  strains,  resulting  from 
the  openings  left  for  the  roadways,  which  seems  more  difficult 
to  guard  against  in  this  design  than  in  that  of  the  cantilever 
presented  by  the  Delaware  Bridge  Company.  It  is  also  more 
difficult  to  erect ;  but,  inasmuch  as  a  responsible  and  well- 
known  company  is  willing  to  undertake  its  construction  and 
erection  for  a  specified  sum,  this  point  possesses  no  special 
significance. 

I  do  not  think  it  safe  to  assume  that  a  clear  height  of  only  120 
feet  at  the  towers,  will  be  all  that  the  general  government  will 
require  at  Blackwell's  Island.  That  height  was  accepted,  it  is 
true,  for  the  Brooklyn  Bridge,  but  the  decision  in  that  case  was 
not  a  general  one. 

Although  it  is  understood  that  Clarke,  Reeves  &  Co.  are  will- 
ing to  raise  the  bridge  at  the  towers  to  a  height  of  130  feet 
above  high  water  without  extra  charge,  if  required  to  do  so, 
their  design  does  not  lend  itself,  as  readily  as  the  cantilever  or 
the  suspension  plans,  to  such  an  increase  of  height. 

While  it  may  be  conceded  that  the  principle  of  the  hinged 
arch  is  applicable  to  longer  spans  than  750  feet,  one  of  the 
advantages  claimed  for  it — that  of  great  economy  of  material — 
would  be  more  largely  realized  in  shorter  than  in  longer  spans. 

By  widening  the  towers,  as  already  suggested,  the  plan 
would,  in  my  judgment,  be  suitable  for  adoption. 

The  design  of  a  cantilever  bridge  submitted  by  the  Delaware 
Bridge  Company  exhibits  an  excellent  application  of  the  prin- 
ciple involved  in  that  method  of  bridge  construction.  The 


37 


centre  of  gravity  is  kept  comparatively  low  (always  a  consider- 
ation of  great  weight)  by  making  all  the  mainstays  parallel  to 
each  other,  and  the  same  with  the  backstays.  The  vertical 
pressures  are  therefore  not  accumulated  at  the  top  of  the  towers. 
But  the  bridge  is,  in  my  judgment,  too  narrow  for  entire  security 
against  wind  pressure,  the  width  of  the  towers  at  the  base, 
for  a  single  track  railroad  being  only  49  feet  over  all,  or  about 
46  feet  between  the  centres  of  the  outer  posts.  The  whole 
system — bridges  and  high  trestles — appears  to  be  deficient  in 
lateral  stability.  By  increasing  the  width  of  the  towers  suffi- 
ciently to  remove  this  serious  objection,  making  them  say  68  or 
70  feet  wide  at  the  base  for  a  single  track  railway,  and  keeping 
the  loot-paths  on  the  same  level  with  the  roadways,  with  other 
changes  of  detail  naturally  resulting  from  these,  the  design  would, 
in  my  judgment,  be  preferable  to  that  of  Clarke,  Reeves  &  Co. 
In  the  design  for  a  single  track  road  as  submitted,  Clarke, 
Reeves  &  Co.'s  two  bridges  cost  $55,599  more,  and  their  whole 
project,  inehiding  approaches,  $11,041  less,  than  in  that  of  the 
Delaware  Bridge  Company.  The  modifications  recommended 
in  the  two  cases  would  make  the  difference  in  total  cost  still 
greater  against  the  Delaware  Bridge  Company  ;  and,  as  you 
would  have  a  good  bridge  in  either  case,  you  would  be  justified 
in  giving  due  weight  to  the  question  of  cost. 

A  cross  section  of  the  modified  towers  for  the  cantilever  design 
might  be  somewhat  like  the  sketch 
on  the  margin,  in  which  a  is  a 
carriageway  and  foot-path,  b  the 
same,  and  c  a  single  track  railway. 
When  a  second  track  is  added  it 
would  be  placed  at  d,  and  the  two 
inclined  tension  members  moved  to  e. 
By  this  method,  or  something  equi- 
valent to  it,  the  weakness  against 
wind  pressure  caused  by  the  roadway 
openings  would  be  entirely  obviated. 

I  think  highly  of  the  plan  for 
a  suspended  girder  prepared  by 
Edward  VV.  Serrell  &  Son,  but  as  I 
am  the  only  member  of  the  Board 
whose  opinion  of  its  merits  places  it  among  the  three  best 


mm. 


38 


designs  submitted  for  competition,  it  seems  unnecessary  for 
me  to  discuss  its  features.  It  is  the  least  costly  project  before 
the  Board,  and  would  most  likely  remain  so,  even  after  certain 
modifications  of  details,  which  appear  to  me  to  be  necessary, 
shall  have  been  provided  for. 

Very  respectfully,  your  obedient  servant, 

Q.  A.  GILLMORE. 


39 


ADDITIONAL  SURVEYS  AND  SPECIFICATIONS. 


[Appendix  No.  i.] 
SPECIFICATIONS  FOR  DESIGNS 

For  a  Bridge  from  the  City  of  New  York  to  Long  Island,  Crossing  over  Blackwell's 

Island. 


The  designs  shall  consist  of : 

i st.  An  approach  on  the  New  York  side  4,580  feet  long,  of  which 
about  1,000  feet  shall  be  in  tunnel,  extending  from  a  connection  with 
the  tracks  of  the  Harlem  Railroad  on  4th  Avenue,  in  the  vicinity  of 
73d  Street,  to  the  crossing  of  Lexington  Avenue  ;  whence  shall  begin 
an  iron  structure,  curving  to  the  centre  of  the  blocks  between  76th  and 
77th  Streets,  and  continuing  eastward  through  the  same  to  the  west 
bank  of  the  western  channel  of  the  East  River. 

2d.  Of  a  single  span  across  the  said  west  channel  734  feet  long  in 
the  clear. 

3d.  Of  an  iron  structure  across  Blackwell's  Island,  about  700  feet 
long. 

4th.  Of  a  single  span  across  the  eastern  channel  of  the  said  East 
River,  618  feet  long  in  the  clear. 

5th.  Of  an  approach  on  the  Long  Island  side,  3,900  feet  long,  ex- 
tending to  the  high  ground. 

The  total  length  of  said  bridge  is  thus  10,532  feet  approximately. 

Spans  of  100  feet  in  the  clear  shall  be  provided  across  the  8  Avenues 
shown  on  the  profile.  The  other  spans  in  the  approaches  and  over 
Blackwell's  Island  may  be  such  as  the  respective  designers  shall  deem 
most  economical. 

There  shall  be  main  approaches  for  carriages ;  and  in  addition 
thereto,  there  shall  be  two  return  auxiliary  approaches  for  carriages, 
ascending  with  gradients  of  4  feet  per  100.  The  return  approach  on 
the  New  York  side  from  the  vicinity  of  Avenue  A,  and  that  on  the 


40 


Long  Island  side  from  the  vicin:ty  cf  Vernon  Avenue,  to  an  intersection 
of  the  main  approaches,  as  shown  on  the  profile. 

There  shall  also  be  two  double  elevators  for  foot  passengers,  with 
the  necessiry  steam  power  ;  one  on  the  New  York  and  the  other  on 
the  Long  Island  shore,  at  or  near  the  end  of  the  bng  spans,  with  a 
capacity  of  30  foot  passengers  per  lilt  platform. 

General  Disposition. 
The  bridge  shall  be  designed  to  accommodate  : 

A.  A  single  track  railway  extending  over  its  entire  length,  and  occu- 
pying a  width  of  14  feet.  To  be  so  arranged  that  a  second  track  can 
be  added  hereafter  without  materially  changing  the  general  arrange- 
ment of  parts  or  the  loads  imposed  upon  them,  or  interfering  with  the 
current  use  of  the  bridge.  A  preference  will  be  given  to  those  designs 
which  make  the  future  addition  of  the  second  track  an  integral  part  of 
the  plan. 

B.  Two  roadways  for  carriages,  extending  from  3d  Avenue  to  the 
high  ground  on  the  Long  Island  side,  each  10  feet  wide,  which  shall 
preferably  be  placed  side  by  side,  and  which  may  be  placed  on  the 
ground  beneath  the  trestle  carrying  the  railway  from  3d  Avenue  to 
2d  Avenue,  on  the  New  York  side,  and  from  the  foot  of  the  grade  (as 
shown  in  the  profile),  to  the  high  ground  on  the  Long  Island  side. 
The  return  approaches  from  Avenue  A,  and  from  Vernon  Avenue, 
may  be  placed  either  side  by  side,  or  separately  on  each  side  ;  but 
should  on  the  Long  Island  side  preferably,  and  peremptorily  on  the 
New  York  side,  be  arranged  within  the  line  of  the  main  trestle  legs, 
so  that  the  same  shall  occupy  as  little  width  as  possible  on  the  ground. 
The  returns,  where  they  join  the  main  approaches,  shall  be  sufficiently 
wide  to  admit  of  an  easy  turn  for  carriages,  and  shall  present  a  level 
grade  for  60  feet. 

C.  Two  sidewalks,  each  5  feet  wide,  extending  either  alongside  or 
overhead  of  the  main  carriageways  or  the  railway,  but  not  along  the 
auxiliary  return  approaches. 

Gradients. 
The  gradients  shall  be  as  follows  : 

On  the  Railway. — The  maximum  grade  shall  be  2-^,,-  feet  per  100, 
or  116  feet  per  mile,  on  the  approaches  on  both  the  New  York  and 
Long  Island  sides,  and  level  across  Blackwell's  Island.  The  end  sup- 
ports of  the  long  spans  shall  be  on  the  san  e  level,  but  there  may  be 
such  camber  in  these  spans,  not  exceeding  a  gradient  of  2f$  feet  per 
100,  as  the  designers  shall  prefer. 


41 


In  each  of  the  long  spans,  the  lowest  part  of  the  bridge  shall  be  135 
feet  in  the  clear  above  mean  high  tide,  at  the  middle  of  the  river. 

On  the  Roadway. — Across  the  long  spans,  and  across  Blackwell's 
Island,  the  roadways  for  carriages  shall  be  on  the  same  floor  as  the 
railway,  thus  requiring  a  total  available  width  of  34  feet.  On  both  the 
direct  and  return  approaches  the  gradients  shall  be  4  feet  per  100  feet, 
with  level  resting  places  as  shown  upon  the  profile. 

A  clear  headroom  of  16  feet  shall  be  allowed  in  all'instances  for  the 
roadway,  and  there  shall  be  a  clear  headway  of  20  feet  above  the  rail- 
way. 

On  the  Sidewalks. — The  grades  on  the  sidewalks  may  be  ar- 
ranged as  most  convenient  to  the  designers.  In  case  of  a  relative 
change  of  level  with  reference  to  the  roadway,  it  will  be  preferred  that 
they  should  be  ramped  to  an  inclination  not  exceeding  1  in  12,  rather 
than  to  resort  to  staircases. 

Foundations  and  Masonry. 

Wherever  practical,  the  design  shall  provide  for  carrying  the  founda- 
tions to  the  rock,  the  approximate  line  of  which  is  shown  upon  the 
profile.  The  masonry  provided  for  shall,  in  all  cases,  be  first-class, 
and  laid  in  hydraulic  cement  mortar.  A  gross  sum  of  $100,000  shall 
be  allowed  by  each  designer  in  his  estimates,  to  cover  the  cost  of  the 
coffer-dams  required  to  lay  the  foundations  for  the  abutments.  These 
latter  shall  consist  of  masonry  from  the  bed  rock  to  a  height  of  at  least 
10  feet  above  mean  high  water ;  above  this  they  may  be  of  masonry, 
or  they  may  be  towers  of  cast-iron,  wrought-iron,  or  mild  steel,  as 
preferred  by  the  designers. 

All  masonry  shall  be  so  designed  that  the  distributed  weight,  in- 
cluding that  of  the  loaded  superstructure,  shall  nowhere  produce  pres- 
sures exceeding  180  pounds  to  the  square  inch,  and  the  foundation 
castings  of  iron  columns  shall  be  proportioned  so  as  to  limit  the  strain 
upon  their  surface  of  contact  with  the  pedestal  stone  to  300  pounds 
per  square  inch. 

Iron  or  steel  used  in  the  towers  shall  be  proportioned  in  accordance 
with  the  specifications  hereinafter  given  for  their  employment  in  the 
other  parts  of  the  bridge. 

Moving  Loads. 

In  addition  to  the  weight  of  the  structure  itself,  and  of  its  floors  and 
appurtenances,  the  following  moving  loads  shall  be  provided  for : 

1st.  For  the  Railway. — Of  two  45-ton  Mogul  locomotives  coupled, 
occupying  each,  with  its  tender,  a  length  of  48  feet,  and  with  75,000 


42 


pounds  on  a  driving  wheel  base  of  1 5  feet,  followed  by  a  train  of  loaded 
freight  cars  weighing  1.500  pounds  per  lineal  foot  of  track.  The 
weights  imposed  by  this  load  upon  different  lengths  of  .track  will  be  as 
follows : 


700  to  800  feet  1,620  pounds  per  lineal  foot. 

oco  "  700  "   1  640       "       "       "  " 

500  "  600  "   1  670  '  

400  "  500  '•   1,710 

300  "  400  "   1,780 

200  ■'  300  "   1  920       "       '■       "  " 

150  "  200  "   2,040       "       "       "  •' 

100  "  150  "   2.34°       "       "       "  " 

80  "  100  "   2,500       "       "       "  " 

60  "    80  "   2,700       "       "       "  " 

40  "    60  "   3,000       "       "       "  " 

25  "    40  "  3  3°° 

15  "    25  "   4,000 

15  feet  or  less  5,000 


In  computing  the  loads  for  distances  very  near  to  the  above  dividing 
points,  varying  weights  per  foot  shall  be  used,  so  that  the  aggregate 
moving  load  shall  never  be  less  than  if  computed  for  a  shorter  dis- 
tance at  the  next  higher  rate  per  foot. 

The  strains  are  to  be  calculated  for  such  position  of  the  driving 
wheels  and  loads  as  will  produce  the  maximum  effect  upon  the  differ- 
ent members. 

2d.  For  the  Roadways. — A  moving  load  shall  be  allowed  of  75 
pounds  per  square  foot,  or  of  750  per  lineal  foot  upon  each  roadway, 
10  feet  wide,  for  all  spans  up  to  100  feet;  for  the  long  spans  across  the 
river,  the  moving  load  shall  be  assumed  at  50  pounds  per  square  foot, 
or  500  per  lineal  foot  of  roadway,  10  feet  wide, 

The  floor  beams  and  joists  shall,  however,  be  calculated  for  a  local 
load  of  100  pounds  per  square  tfoot.  The  floor  of  the  roadway  shall 
consist  of  oak  plank  3  inches  thick,  with  suitable  guards,  and  the  main 
floor  beams  shall  be  of  wrought-iron. 

3d.  For  the  Sidewalks. — A  moving  load  shall  be  assumed  of  75 
pounds  to  the  square  foot,  or  of  375  pounds  per  lineal  foot  upon  each. 
The  floor  shall  be  laid  with  2-inch  Southern  pine,  surfaced,  and  with 
suitable  railing  and  guards. 

The  points  of  application  of  these  various  moving  loads  on  the  tres- 
tles are  indicated  by  the  gradients  on  the  profile.  The  designs  shall 
show  how  it  is  proposed  to  provide  for  the  second  railway  track. 

Strains  Allowed. 

In  every  case  the  plans  shall  provide  for  the  maximum  strain  which 
can  by  any  possibility  come  upon  each  part  of  the  structure. 

All  its  parts  shall  be  so  designed  that  the  strains  coming  upon  them 


43 


can  be  accurately  calculated  by  the  usual  formulae  recognized  as  cor- 
rect by  bridge  engineers. 

The  strains  arising  from  the  wind  shall  be  calculated  upon  two  sup- 
positions:  ist.  That  the  various  parts  of  the  bridge  are  fully  loaded 
with  the  assumed  rolling  loads,  and  that  the  wind  exerts  a  pressure  of 
24  pounds  per  square  foot,  at  right  angles  to  the  bridge  line,  upon  the 
exposed  surface  of  the  structure,  and  of  a  train  of  cars  10  feet  high 
standing  thereon.  2d.  That  the  wind  exerts  a  pressure  of  40  pounds 
per  square  foot  at  right  angles,  upon  the  exposed  surface  of  the  un- 
loaded bridge. 

For  both  of  these  supposed  cases,  the  factor  of  safety  shall  be  3,  and 
the  base  of  the  trestles  shall  be  spread  so  wide  as  to  counteract  all 
tendency  to  overturning. 

Changes  of  temperature  to  the  amount  of  150  degrees  shall  be  pro- 
vided for,  and  the  parts  so  designed  as  to  admit  of  expansion  and 
contraction,  and  to  provide  for  the  strains  resulting  therefrom. 

The  various  spans  shall  be  so  designed  that  their  deflection,  under 
the  assumed  maximum  moving  load  and  strains,  shall  not  exceed 
the  Tiou  part  of  their  length.  The  side  deflection  or  motion  from  the 
assumed  wind  effects  shall  be  limited  to  the  tuu  part  of  the  spans,  and 
in  both  cases  the  parts  shall  be  so  proportioned  as  to  return  to  their 
original  line  after  the  load  is  withdrawn. 

Tension  Members. — f  or  the  weight  of  the  structure,  for  the  effects 
of  the  wind  and  of  changes  of  temperature,  a  factor  of  safety  of  three 
(3)  shall  be  adopted,  while  for  the  rolling  or  live  load  the  factor  of 
safety  shall  be  eight  (8). 

The  amount  of  material  in  the  several  parts  of  the  structure  shall  be 
proportioned  for  these  combined  factors  of  safety  ;  that  is  to  say,  that  if 
it  is  desired  to  use  in  a  part  strained  in  tension,  double  rolled  refined 
iron,  with  an  ultimate  breaking  strength  of  54,000  pounds  per  square 
inch,  in  long  specimens,  this  may  be  strained  up  to  18,000  pounds  per 
square  inch  if  it  carries  only  dead  load,  or  up  to  6,750  pounds  per 
square  inch  if  only  exposed  to  live  load. 

The  size  or  sectional  area  of  the  various  members  in  tension  shall, 
therefore,  be  ascertained  by  adding  to  the  number  of  inches  required  to 
carry  the  dead  load  at  the  rate  of  18,000  pounds,  the  number  of  inches 
required  to  carry  the  live  load,  at  the  rate  of  6750  pounds  per  square 
inch.* 

In  proportioning  the  parts  for  the  combined  dead  and  live  loads,  re- 
gard shall  be  had  to  the  frequency  with  which  the  estimated  load  is 


*Note. — The  average  effect  of  these  combined  strains  will  be  as  follows  : 

ist.    When  dead  load  =  2  live  loads — an  average  strain  of  14,250  pounds  per  square  inch. 

*d.    When  dead  load  =  live  load — an  average  strain  of  12,375  pounds  per  inch. 

3d.    When  dead  load  -      live  load — an  average  strain  of  10,500  pounds  per  square  inch 


44 


like.y  to  be  imposed  in  working,  and  a  greater  proportional  strength 
shall  be  allowed  for  parts  likely  to  be  strained  to  the  calculated  intens- 
ity by  every  passing  train  or  carriage,  than  for  those  upon  which  the 
assumed  load  can  only  come  occasionally  ;  thus,  iron  floor-beams  and 
floor-hangers  shall  only  be  strained  up  to  6,750  pounds  per  square  inch, 
while  chord-bars  may  be  strained  up  to  the  full  average  obtained  from 
the  combined  dead  and  live  loads.  No  part  less  than  5  feet  long  shall 
be  strained  in  tension  more  than  7,000  pounds  to  the  inch. 

All  tensile  members  shall  be  preferably  of  refined  wrought-iron,  of 
soft,  fibrous  texture,  rolled  twice  from  the  puddle-bar,  with  an  ultimate 
breaking  strength  of  at  least  50,000  pounds  per  square  inch  in  long 
specimens,  and  an  elastic  limit  of  not  less  than  26,000  pounds  per 
square  inch.  It  shall  elongate  at  least  fifteen  per  cent  before  break- 
ing, and  the  elastic  limit  shall  be  understood  to  be  the  point  at  which 
the  elongation  produced  by  the  strain  ceases  to  increase  in  the  same 
proportion  as  the  strain,  being  the  point  at  which  the  bar  shows  the 
first  signs  of  a  considerable  permanent  set. 

If  designers  propose  to  use  steel  in  tension,  they  will  be  required  to 
furnish  evidence  of  its  adaptability  for  this  purpose,  both  as  regards  its 
resistance  to  tensile  strains,  to  impacts  and  repeated  vibrations,  as  well 
as  to  the  absolute  certainty  of  uniformity  in  its  production,  as  ascer- 
tained by  "experiment. 

Compression  Members  may  be  of  cast  or  wrought-iron,  or  of  mild 
steel. 

For  wrought-iron,  when  the  length  of  square  end  pillars  does  not  ex- 
ceed twenty-four  times  the  least  radius  of  gyration,  the  part  may  be 
subjected  to  a  strain  of  8,000  pounds  to  the  square  inch. 

When  the  member  has  a  greater  proportional  length,  its  size,  if  of 
wrought-iron,  shall  be  determined  by  Gordon's  formula  for  square  end 
pillars,  in  the  following  modified  form. 

40,000 

F—  

l2 

T    +  ■ 

40,000  ra 

In  which  P  denotes  the  ultimate  strength  per  square  inch  of  section,  / 
the  length,  and  r  the  least  "  radius  of  gyration  "  of  cross  section, 

For  this  ultimate  strength  a  factor  of  safety  shall  be  used,  of  3  for 
the  dead  load,  and  of  6  for  the  live  load,  or  the  equivalent  dead  load  of 
both  combined  shall  be  arrived  at  by  the  formula  : 

3  dead  load  +  6  live  load 

 =  equivalent  dead  load. 

3 

For  which  the  factor  of  safety  shall  be  3.  From  the  results  thus  ob- 
tained, twenty  (20)  per  cent  shall  be  deducted  for  each  pin-joint  in  a 
strut  or  post. 


45 


A  preference  will  be  had  for  those  shapes,  in  compression  members, 
which  are  most  accessible  for  inspection,  cleaning  and  painting. 

Designers  who  propose  to  employ  steel  in  compression  will  be  required 
to  furnish  evidence  based  upon  reliable  experiments,  that  the  strains 
which  they  propose  to  impose  upon  it  are  relatively  as  safe  as  those 
herein  provided  for  wrought-iron,  and  of  the  absolute  certainty  of  uni- 
formity in  its  strength,  as  ascertained  by  experiment. 

In  the  absence  of  such  proof,  strains  allowed  upon  steel  shall  not  be 
more  than  20  per  cent  in  excess  of  those  which  would  be  allowed  upon 
wrought-iron. 

Cast-iron  shall  not  be  used  for  the  principal  members  of  the  trussed 
spans.  It  shall  be  proportioned  for  compression  by  Rankine's  modifi- 
cation of  Gordon's  formula,*  with  a  factor  of  safety  of  4  for  the  dead 
load,  and  of  8  for  the  live  load.  No  cast-iron  part  shall  be  designed  to 
be  less  than  }i  of  an  inch  thick,  nor  shall  it  be  used  where  it  is  liable  to 
receive  a  transverse  or  a  tensile  strain,  or  where  there  is  any  probability 
that  the  shape  of  the  parts  will  cause  imperfections  in  the  castings, 
such  as  floating  of  cores,  blow- holes,  &c. 

Strain  sheets  are  to  be  furnished  for  the  examination  of  the  engineers, 
showing  separately  the  strains  due  to  the  dead  and  to  the  live  load,  as 
well  as  those  due  to  the  wind,  and  to  changes  of  temperature. 

Estimates  of  weights  and  cost  shall  be  required  in  sufficient  detail  to 
admit  of  their  accuracy  being  tested,  showing  both  the  quantities  of  each 
kind  of  materials,  and  the  prices  at  which  the  designers  propose  to  fur- 
nish them  erected  in  place. 

Details  of  Construction. 

The  erection  of  the  structure  shall  be  so  designed  as  not  to  interrupt 
the  navigation  of  the  East  River,  or  the  use  of  any  public  road,  street 
or  avenue. 

A  preference  will  be  given  to  those  designs  which,  at  an  equal  cost, 
occupy  the  least  width  on  the  ground  on  the  New  York  side,  so  as  to 
reduce  the  cost  of  land  damages. 

The  designs  shall  be  based  upon  the  use  of  the  best  quality  of 
materials. 

Cast-iron  may  be  used  in  towers,  bed-plates,  pedestals  and  washers. 
It  shall  be  of  the  best  quality  of  soft  gray  iron. 

A  preference  will  be  had  for  upset  ends  in  all  tension  members. 
Where  welds  are  proposed  to  be  used  by  the  designeis,  a  statement  will 


80,000 

*NOTE. — P=  

I  +  

3200  r'2 


46 


be  required  of  the  mode  in  which  it  is  proposed  to  make  these  welds, 
and  to  prove  their  workmanship. 

Rivet-holes  in  wrought-iron  members  may  be  punched,  but  an  accu- 
rate fit  will  be  required.  All  other  holes  shall  be  drilled.  The  enlarged 
ends  of  eye-bars  shall  be  of  such  form  that  the  cross  section  of  metal 
in  the  head,  exclusive  of  the  pin-hole,  shall  be  fifty  per  cent  in  excess  of 
that  in  the  body  of  the  bar.  The  pin-holes  shall  be  bored  so  that  the 
bars  shall  not  vary  in  length  more  than  1-64  of  an  inch. 

Pins  shall  be  of  wrought-iron,  and  shall  be  turned  to  fit  the  pin-hole 
within  1-32  of  an  inch.  They  shall  be  of  such  section  that  the  shearing 
strain  shall  not  exceed  7,000  pounds  to  the  square  inch,  and  their  diame- 
ter shall  not  be  less  than  two-thirds  of  the  largest  dimension  of  any  ten- 
sion member  attaching  to  them.  It  will  be  preferred  that  all  the 
various  members  attaching  to  pins  shall  be  arranged  as  compactly 
as  possible. 

All  screw  connections  shall  be  enlarged  to  such  diameter  as  to  pro- 
vide for  an  excess  of  material  of  ten  per  cent  after  deducting  the  depth 
of  the  screw  thread,  with  nuts  of  equivalent  strength,  and  shall  have  at 
least  3  threads  projecting  beyond  the  nuts. 

All  details  of  manufactured  bars  shall  be  of  such  sufficient  strength, 
that,  upon  being  tested,  fracture  shall  sooner  occur  in  the  body  of  the 
bar  than  in  any  of  its  connection  details. 

No  wrought-iron  cr  steel  shall  be  used  less  than  of  an  inch  thick, 
except  in  places  where  both  sides  are  always  accessible  for  cleaning 
and  painting,  or  where  the  entire  surface  is  bedded  in  some  non-corro- 
sive material. 

Designs  may  provide  for  a  wooden  trestle  on  the  Long  Island  side,  as 
far  as  the  same  may  be  more  economical  than  iron  ;  so  arranged  as  to 
admit  of  the  timber  being  renewed  piece-meal  as  it  decays. 


0.  CHANUTE,  ) 

I  G.  BARNARD,  >  Consultitig  Engineers. 
Q.  A.  GILLMORE,  ) 


47 


[Appendix  No.  3.] 

New  York,  May  1,  1876. 

M  

The  undersigned,  aboard  of  consulting  engineers,  appointed  by  the 
New  York  and  Long  Island  Bridge  Company  to  select  a  plan  for  its 
proposed  bridge  crossing  the  East  River  at  Blackwell's  Island,  will  re- 
ceive designs,  estimates  of  cost,  and  proposals  for  construction,  until 
the  1  st  day  of  July,  1876,  for  a  bridge  and  its  approaches  from  the  City 
of  New  York,  in  the  vicinity  of  76th  street,  to  Long  Island. 

This  will  require  two  spans  across  the  East  River,  135  feet  above 
tide  ;  the  one  734  feet  long,  and  the  other  618  feet  long,  in  the  clear  ; 
together  with  approaches  and  an  intermediate  structure  across  Black- 
well's  Island  over  100  feet  high. 

We  herewith  inclose  a  profile  and  specifications,  and  will  be  pleased 
to  receive  designs,  estimates,  and  a  proposal  for  building,  from  you. 

Parties  who  have  already  furnished  designs  to  the  Company  are  re- 
quested to  revise  them  so  as  to  conform  to  the  present  specifications, 
and  to  furnish  new  estimates  of  cost  and  proposals  for  construction. 

The  adoption  of  a  plan  shall  not,  however,  be  understood  as  binding 
the  Company  to  enter  into  an  immediate  contract  for  the  prosecution 
of  the  work,  and  the  right  is  reserved  to  reject  any  or  all  proposals  or 
plans. 

It  is  expected  that  the  designs  received  in  answer  to  this  circular 
shall  be  exhibited  at  the  Centennial  Exhibition,  unless  otherwise  re- 
quested by  the  designers. 

Plans  and  communications  may  be  sent  to  the  undersigned  either  at 
their  respective  offices,  or  at  the  office  of  the  Company  in  the  German 
Savings  Bank  Building,  corner  of  14th  Street  and  4th  Avenue. 

O.  CHANUTE,  Erie  Railway,  New  York. 

J.  G.  BARNARD,  Army  Building,  New  York. 

Q.  A.  GILLMORE,  Army  Building,  New  York. 

Consulting  Engineers, 


48 


[Appendix  No.  4.] 

New  York,  August  11.  1876. 

M  

At  a  regular  meeting  of  the  Board  of  Directors  of  the  New  York 
and  Long  Island  Bridge  Company,  held  on  the  9th  of  August,  1876,  it 
was  resolved  : 

"  That  the  time  for  receiving  plans  be  extended  to  December  i,  1876,  and  that 
the  engineers  give  notice,  with  a  view  of  bringing  out  the  best  talent  in  the  coun- 
try, that  this  company  will  pay  to  the  party  whose  plan  shall  be  adopted  as  the 
best,  the  sum  of  one  thousand  dollars  ;  for  the  second  best,  five  hundred  dollars  ; 
and  for  the  third,  two  hundred  and  fifty  dollars.  Plans  so  paid  for  to  be  the  prop- 
erty of  the  company.  The  awards  to  be  made  by  this  Board,  under  advisement  of 
the  consulting  engineers." 

Please  advise  us  at  your  earliest  convenience  whether  you  shall  com- 
pete for  the  above  premiums,  under  the  general  requirements  of  our 
circular  and  specifications  of  May  1st. 


O.  CHANUTE,  ) 

J.  G.  BARNARD.  \  Consulting  Engineers. 
O.  A.  GILLMORE,  ) 


IRE  FliOrOSED 


BRIDGE  AF 
ISLAJS'D. 


BLA  CK  WELL'S 


DISSATISFACTION  WITH   TnK  AWARD  OF  PRIZES  FOR 
THE  PLANS  OF  THE  STRUCTURE. 

As  the  construction  of  this  bridge  will  gofartovrard 
soling  the  question  of  fiuding  cheap  suburban 
homes  wit  hin  easy  reach  of  the  business  portion  of 
Now- York,  everything  concerning  it  must  possess 
great  interest  to  citizens.  The  Tribune  pub- 
lished a  few  weeks  ago  a  diagram  of  the  plan  to 
which  the  directors  of  the  company  had  awarded  the 
first  premium  of  $1,000,  and  also  a  synopsis  of  the 
report  of  the  consulting  engineers.  It  has  since 
been  ascertained  that  much  dissatisfaction  exists  at 
this  award,  which  was  given  to  the  plan  of  the 
Delaware  Bridge  Co.,  designed  by  Mr.  McDonald, 
C.  E.  The  following  is  the  substance  of  the  resolu- 
tion of  the  board  of  directors  inviting  the  submis- 
sion of  plans  : 

Resolved,  *  *  *  -with  a  view  of  bringing  out  the  beet 
talent  in  tiie  country,  that  this  company  will  pay  to  the 
party  whose  plan  shall  be  adopted  as  the  beet  the  sura 
of  $1,000;  for  tae  second  best,  $500.  and  for  the  third, 
$250.  *  *  *  Awards  to  be  made  by  tnis  board,  under 
advisement  of  the  consulting  engineers. 

The  commission  of  consulting  engineers  to  whom 
the  plans  were  referred  consisted  of  Gens.  J.  G.  Bar- 
nard and  Q.  A.  Gill  more,  United  States  Engineers, 
and  Mr.  O.  Chanute,  C.  E.  These  gentlemen  made  a 
joint  report,  iu  which,  referring  to  their  individual 
views  as  to  the  merits  of  the  various  plans,  they 
make  the  following  statement : 

Two  out  of  the  three  pronounce  the  nlan  of  Clarke, 
Reeves  <fe  Co.  the  best,  if  taken  absolutely" without  modi- 
fication, and  entirely  with  reference  to  its  strain  sheets 
and  specifications  ;  while  two  out  of  three  pronounce  tne 
Delaware  Bridge  Company's  plan  "best"  to  recommend 
to  be  adopted  for  practical  construction  by  your  com- 
pany, with  such  improvements  and  modifications  as 
suggest  themselves. 

The  resolution  of  the  Board  of  Directors  clearly 
indicated  that  the  first  prize  would  be  awarded  to 
the  best  plan  submitted,  aud  not  to  a  second-rate 
one  which  the  consulting  engineers,  after  careful 
examination  of  all  the  others,  might  improve  by  their 
own  suggestions,  and  thus  make  it  virtually  a  plan 
of  the  judges  "themselves.  There  would  certainly 
be  only  little  inducement  to  present  a  care- 
fully matured  plan,  which  would  probably 
cost  nearly  or  quite  as  much  as  the  highest 
premium  offered,  if  the  awards  were  not  to  be  made 
on  the  merits  of  it,  as  submitted.  Messrs.  Barnard 
and  Gillmoro  made  separate  reports  in  addition  to 
the  joint  one  made  by  the  three  consulting  en- 
gineers. Gen.  Barnard  strongly  urged  the  plan  of 
Clarice,  Reeves  &  Co.  as  greatly  superior  to  all  the 
others,  modified  or  unmodified ;  while  Gen.  Gillmore 
says  of  it,  "  The  design  of  Clarke,  Beeves  &  Co.  is 
the  only  one  submitted  to  us  that  1  would  be  willing 
to  recommend  for  adoption  by  your  company  as  it 
stands,  and  without  modification."  The  award  of 
the  first  premium  to  the  Delaware  Bridge  Company 
by  the  Directors,  in  view  of  their  resolution  inviting 
plans,  and  taken  in  connection  with  the  views  ex- 


pressed by  two  of  the  three  consulting  engineers, 
sreated  much  surprise  at  the  time,  and  a  subsequent 
development  of  facts  has  caused  this  feeling  to  grow 
into  one  of  decided  dissatisfaction  among  some  of 
those  who  desire  the  construction  of  a  first-class 
structure. 

When  the  commission  of  engineers  waited  in  per- 
son upon  the  Board  of  Directors  with  their  report 
they  were  told  that  no  action  would  be  taken  on  it 
until  it  was  printed,  and  that  when  this  was  done 
they  would  be  asked  to  come  before  the  board  for 
advisement,  as  provided,  in  the  resolution  above 
quoted.  When  the  report  was  printed,  however,  a 
special  meeting  of  the  board  was  held,  at  which  a 
bare  quorum  was  present.  Gens.  Barnard  aud  Gill- 
more  were  not  notified  to  be  present,  but  Mr. 
I  Chanute  was  on  hand,  and  without  any  refcrenco  of 
,  this  important  subiect  to  a  committee,  without  cou- 
'  suiting  any  engineer  except  Mr.  Chanute,  who  advo- 
cated the  Delaware  Bridge  Company's  plan,  and 
without  waiting  for  the  regular  monthly  meeting, 
the  directors  present  awarded  the  first  premium  to 
that  company,  the  second  one  to  Clarke,  Reeves  <feCo., 
and  the  third  one  to  Henry  Flad  &  Co.,  and, 
it  is  understood,  by  resolution  adopted  the  plan 
of  the  Delaware  Bridge  Company  as  the  one  on 
!  which  the  bridge  should  be  constructed. 

There  is  little  or  no  difference  in  the  cost  of  the 
plans  proposed  by  the  Delaware  Bridge  Company 
and  that  of  Clarke,  Reeves  &  Co.  The  first  is 
known  as  a  "  cantilever,"  with  an  intermediate 
truss  200  feet  long  in  the  middle  of  the  span,  which 
truss  is  supported  on  the  two  ends  of  the  canti-. 
levers.  Clarke,  Reeves  &  Co.  propose  an  arch 
which  springs  from  the  natural  rock  foundation  on 
the  main  shore,  with  a  single  span  of  1,030  feet,  to 
the  natural  rock  on  Blackweli's  Island.  The  arch 
is  ptirabolic  in  form,  and  for  boldness  and  beauty 
of  design  surpasses  anything  of  the  kind  in  the 
world.  The  center  of  the  arch  is  about  200  feet 
high  above  the  river.  Iron  towers  rising  from  the 
water's  edge  on  each  shore,  with  a  clear  opening  of 
734  feet  between  them,  are  secured  to  the  arch  and 
virtually  reduce  its  span  to  this  width,  as  the  por- 
tions of  the  arch  from  the  tops  of  these  towers  to 
the  rock  and  the  towers  themselves  constitute 
in  reality  the  abutments  of  the  arch  proper. 
If  the  selection  of  a  design  for  the  bridge  only  con- 
cerned the  competitors  for  the  premiums  it  would 
be  a  matter  of  small  moment,  but  as  the  public  are 
deeply  interested  in  the  early  election  of  a  thor- 
oughly substantial  structure,  they  have  a  right  to 
criticise  the  informal  and  hasty  action  of  the  direc- 
tors in  a  decision  which,  by  inviting  capitalists  to 
invest  their  money  upon  a  plan  as  yet  not  only  un- 
tried but  condemned  in  strong  language  by  Gen. 
Barnard  in  his  supplementary  report,  delays  the 
time  when  the  shores  of  New-York  and  Long  Island 
will  be  connected  by  a  steam  railway  bridge,  and 
rapid  transit  be  obtained  to  the  cheap  and  sparsely 

\ settled  section  adjacent  to  the  other  end  of  the  pro- 
posed structure.  


